IB Biology textbook

Dg\Vc^X VcY ^cdg\Vc^X XdbedjcYh

$IFNJDBM DPNQPVOET BSF EJWJEFE JOUP UXP HSPVQT PSHBOJD BOE JOPSHBOJD
0SHBOJD DPNQPVOET JODMVEF BMM UIF DPNQMFY DPNQPVOET PG DBSCPO GPVOE
JO MJWJOH PSHBOJTNT
CVU OPU TJNQMF DBSCPO DPOUBJOJOH DPNQPVOET TVDI BT
DBSCPO EJPYJEF
DBSCPOBUFT BOE IZESPHFODBSCPOBUFT 5IFTF BOE BMM PUIFS
DPNQPVOET BSF JOPSHBOJD #PUI HSPVQT BSF GPVOE JO MJWJOH PSHBOJTNT

7j^aY^c\ WadX`h d[ dg\Vc^X bdaZXjaZh

.BOZ PSHBOJD NPMFDVMFT BSF WFSZ MBSHF BOE DPNQMFY CVU UIFZ BSF CVJMU VQ
PG TNBMM TVCVOJUT
XIJDI DBO CF SFMBUJWFMZ TJNQMF 'JHVSF 3.4 TIPXT TPNF
PG UIFTF CVJMEJOH CMPDLT 4VCVOJUT DBMMFE NPOPNFST BSF CVJMU JOUP DPNQMFY
QPMZNFST

8='D= I]Z [djgi] WdcY ^c Vc Vb^cd VX^Y XVc WZ id
Vcn dcZ d[ V l]daZ gVc\Z d[ Y^[[ZgZci \gdjeh#

I]Z aZiiZg G ^h jhZY id h]dl i]^h \gdje#

= 8 D = Vb^cd \gdje XVgWdmna \gdje
=GD
8 = 8 C8 8
D= =
=D

=D 8 8 D= = = D= 8=' D D=

= D= Vb^cd VX^Y 8= =8
=8 8=
\ajXdhZ

= == = = = = = = = = = = = D D= D=
8 8 8 8 8 8 8 8 8 8 8 8 8 8 D=
g^WdhZ
=
= == == == == == =

[Viin VX^Y

;^\jgZ (#) I]Z WVh^X higjXijgZh d[ \ajXdhZ! Vb^cd VX^Yh! [Viin VX^Yh VcY g^WdhZ Ä i]Z Wj^aY^c\ WadX`h d[ dg\Vc^X bdaZXjaZh#

8VgWd]nYgViZh

Carbohydrates DPOUBJO POMZ DBSCPO
IZESPHFO BOE PYZHFO BOE UIFZ
BSF UIF NPTU BCVOEBOU DBUFHPSZ PG NPMFDVMF JO MJWJOH UIJOHT *O CPUI
QMBOUT BOE BOJNBMT UIFZ IBWF BO JNQPSUBOU SPMF BT B TPVSDF PG FOFSHZ

BOE JO QMBOUT UIFZ BMTP IBWF B TUSVDUVSBM GVODUJPO $BSCPIZESBUFT PDDVS
JO EJĄ FSFOU GPSNT monosaccharides
XIJDI DPOUBJO POMZ POF TVCVOJU
disaccharides
XIJDI IBWF UXP BOE polysaccharides
XIJDI BSF GPSNFE
GSPN MPOH DIBJOT PG NPOPTBDDIBSJEFT 5BCMF 3.3 PWFSMFBG
TIPXT FYBNQMFT
PG DBSCPIZESBUFT BOE UIFJS VTFT

8dcYZchVi^dc VcY ]nYgdanh^h

*O B condensation reaction
UXP NPMFDVMFT DBO CF KPJOFE UP GPSN
B MBSHFS NPMFDVMF
IFME UPHFUIFS CZ TUSPOH covalent bonds &BDI
DPOEFOTBUJPO SFBDUJPO SFRVJSFT BO FO[ZNF UP DBUBMZTF UIF QSPDFTT

( I=: 8=:B>HIGN D; A>;: )(

;dgb d[ :mVbeaZh :mVbeaZ d[ jhZ ^c eaVcih :mVbeaZ d[ jhZ ^c Vc^bVah
XVgWd]nYgViZ

bdcdhVXX]Vg^YZ \ajXdhZ! \VaVXidhZ! [gjXidhZ ^h V XdbedcZci d[ [gj^ih! bV`^c\ \ajXdhZ ^h i]Z hdjgXZ d[ ZcZg\n [dg XZaa

[gjXidhZ i]Zb iVhiZ hlZZi VcY ViigVXi^c\ Vc^bVah id gZhe^gVi^dc Ä ^i ^h dWiV^cZY [gdb i]Z

ZVi i]Zb! i]ZgZWn Y^heZgh^c\ i]Z hZZYh ^ch^YZ Y^\Zhi^dc d[ XVgWd]nYgViZ [ddYh

Y^hVXX]Vg^YZ bVaidhZ! aVXidhZ! hjXgdhZ ^h igVchedgiZY [gdb aZVkZh id hidgV\Z aVXidhZ ^h [djcY ^c b^a` VcY egdk^YZh
hjXgdhZ i^hhjZh VcY di]Zg eVgih d[ i]Z eaVci id egdk^YZ ZcZg\n [dg ndjc\ bVbbVah
Vc ZcZg\n hdjgXZ

edanhVXX]Vg^YZ hiVgX]! \anXd\Zc! XZaajadhZ ^h V higjXijgVa XdbedcZci d[ eaVci \anXd\Zc ^h i]Z hidgV\Z XVgWd]nYgViZ d[
XZaajadhZ XZaa lVaah Vc^bVah! [djcY ^c i]Z a^kZg VcY bjhXaZh
hiVgX] ^h jhZY Vh V [ddY hidgZ

IVWaZ (#( :mVbeaZh VcY gdaZh d[ XVgWd]nYgViZh#

BOE JU QSPEVDFT POF NPMFDVMF PG XBUFS 5IF DPOEFOTBUJPO PG UXP
NPOPTBDDIBSJEFT QSPEVDFT B EJTBDDIBSJEF 'PS FYBNQMF

HMVDPTF HBMBDUPTF n MBDUPTF XBUFS
NPOPTBDDIBSJEF
NPOPTBDDIBSJEF
EJTBDDIBSJEF


*G GVSUIFS NPOPTBDDIBSJEFT BSF BEEFE UP B EJTBDDIBSJEF
B QPMZTBDDIBSJEF JT
GPSNFE
BT ZPV DBO TFF JO 'JHVSF 3.5

ild \ajXdhZ bdcdbZgh bVaidhZ Ä V Y^hVXX]Vg^YZ

8='D= 8='D= 8='D= 8='D=

= 8D == 8D == 8D == 8D =

8 = 8 8 = 8 8 = 8 8 = 8
D= = D= = D= = D= =

=D 8 8 D= =D 8 8 D= =D 8 8 D 88 D=

= D= = D= = D= = D=

='D XdcYZchVi^dc gZVXi^dc

dcZ bdaZXjaZ d[
lViZg ^h gZaZVhZY

higjXijgZ d[ eVgi d[ V \anXd\Zc bdaZXjaZ
Ä dcZ edanhVXX]Vg^YZ d[ \ajXdhZ

<anXd\Zc Xdch^hih d[ XdbeVXi
bdaZXjaZh bVYZ je d[
WgVcX]^c\ X]V^ch d[ \ajXdhZ#

;^\jgZ (#* BdcdhVXX]Vg^YZ hjWjc^ih \ajXdhZ ^c i]^h XVhZ VgZ _d^cZY ^c V XdcYZchVi^dc gZVXi^dc! [dgb^c\ V Y^hVXX]Vg^YZ bVaidhZ VcY
lViZg# <anXd\Zc ^h V edanhVXX]Vg^YZ! [dgbZY [gdb adc\ X]V^ch d[ \ajXdhZ hjWjc^ih#
))

Vb^cd VX^Y Vb^cd VX^Y Y^eZei^YZ

= G D= G D = G D G D
C 8 8
C8 8 C8 8 = 8C8
= D=
= = D= = = D= ==

dcZ bdaZXjaZ d[ XdcYZchVi^dc gZVXi^dc
lViZg ^h gZaZVhZY
='D

;^\jgZ (#+ Ild Vb^cd VX^Yh XdbW^cZ id [dgb V Y^eZei^YZ#

*O B TJNJMBS XBZ
UXP BNJOP BDJET DBO CF MJOLFE UP GPSN B dipeptide
'JHVSF 3.6


BNJOP BDJE BNJOP BDJE n EJQFQUJEF XBUFS

8IFO NPSF UIBO UXP BNJOP BDJET BSF KPJOFE JO UIJT XBZ
B polypeptide JT
GPSNFE 1PMZQFQUJEF DIBJOT GPSN QSPUFJO NPMFDVMFT

*O BOPUIFS DPOEFOTBUJPO SFBDUJPO
HMZDFSPM MJOLT UP GBUUZ BDJET UP
QSPEVDF USJHMZDFSJEF lipid NPMFDVMFT 'JHVSF 3.7


HMZDFSPM GBUUZ BDJET n USJHMZDFSJEF MJQJE XBUFS

[Viin VX^Y \anXZgda

= == = = = = = = = = = = = D =
8 8 8 8 8 8 8 =D 8 =
= 8 8 8 8 8 8 8 D=
=D 8 =
= = = = = = = = = = = = XdcYZchVi^dc
=D 8 =
gZVXi^dc =

dcZ bdaZXjaZ d[ lViZg ^h ='D
gZaZVhZY [dg ZVX] [Viin VX^Y

i]Vi XdbW^cZh l^i] \anXZgda

:VX] d[ i]Z ÄD= \gdjeh ^c \anXZgda ^h VWaZ id
XdbW^cZ l^i] i]Z Ä8DD= \gdje d[ V [Viin VX^Y#

D=

8DD 8 =

8DD 8 =

8 D8 =

ig^\anXZg^YZ a^e^Y bdaZXjaZ =

;^\jgZ (#, =dl V ig^\anXZg^YZ a^e^Y ^h [dgbZY [gdb \anXZgda VcY i]gZZ [Viin VX^Yh ^c V XdcYZchVi^dc gZVXi^dc#

( I=: 8=:B>HIGN D; A>;: )*

BdaZXjaZ 6eegdm^bViZ ZcZg\n Hydrolysis reactions PDDVS FWFSZ UJNF GPPE JT EJHFTUFE 5IFTF SFBDUJPOT
XdciZci eZg \gVb $ `? JOWPMWF CSFBLJOH EPXO QPMZTBDDIBSJEFT
QPMZQFQUJEFT BOE USJHMZDFSJEFT
JOUP UIF TNBMMFS VOJUT PG XIJDI UIFZ BSF NBEF 8BUFS NPMFDVMFT BSF VTFE JO
XVgWd]nYgViZ &, IZESPMZTJT SFBDUJPOT m UIFZ BSF UIF SFWFSTF PG DPOEFOTBUJPO SFBDUJPOT 0ODF
a^e^Y (. BHBJO
FO[ZNFT BSF SFRVJSFE UP DBUBMZTF UIF SFBDUJPOT
egdiZ^c &-
r )ZESPMZTJT PG TUBSDI B QPMZTBDDIBSJEF
VTFT XBUFS BOE QSPEVDFT NBOZ

NPMFDVMFT PG HMVDPTF

r )ZESPMZTJT PG QSPUFJO NBEF PG QPMZQFQUJEF DIBJOT
VTFT XBUFS BOE

QSPEVDFT NBOZ BNJOP BDJET

r )ZESPMZTJT PG B USJHMZDFSJEF B MJQJE
VTFT XBUFS BOE QSPEVDFT GBUUZ BDJET

BOE HMZDFSPM NPMFDVMFT

A^e^Yh

-JQJET BSF VTFE BT FOFSHZ TUPSBHF NPMFDVMFT JO QMBOUT BOE BOJNBMT
5SJHMZDFSJEF MJQJET UIBU BSF TPMJE BSF HFOFSBMMZ SFGFSSFE UP BT GBUT
XIJMF JO
MJRVJE GPSN USJHMZDFSJEFT BSF LOPXO BT PJMT "OJNBMT TUPSF FOFSHZ BT GBU
XIFSFBT QMBOUT TUPSF PJMT m GPS FYBNQMF
MJOTFFE PJM BOE PMJWF PJM -JQJE
DPOUBJOT BCPVU UXJDF BT NVDI FOFSHZ QFS HSBN BT DBSCPIZESBUF CVU FBDI
UZQF PG TUPSBHF NPMFDVMF IBT JUT PXO BEWBOUBHFT

r -JQJET DPOUBJO NPSF FOFSHZ QFS HSBN UIBO DBSCPIZESBUFT
TP MJQJE TUPSFT

BSF MJHIUFS UIBO DBSCPIZESBUFT TUPSJOH BO FRVJWBMFOU BNPVOU PG FOFSHZ

r -JQJET BSF BMTP MFTT EFOTF UIBO XBUFS
TP GBU TUPSFT IFMQ MBSHF BRVBUJD

BOJNBMT UP ë PBU

r -JQJET BSF OPO QPMBS
JOTPMVCMF NPMFDVMFT TP UIFZ EP OPU BĄ FDU UIF

NPWFNFOU PG XBUFS JO BOE PVU PG DFMMT CZ PTNPTJT

r -JQJET BSF BMTP JNQPSUBOU JO QSPWJEJOH IFBU JOTVMBUJPO 'BU TUPSFE VOEFS

UIF TLJO SFEVDFT IFBU MPTT BOE JT WJUBM GPS BOJNBMT
TVDI BT TFBMT
QPMBS
CFBST BOE XIBMFT
XIJDI MJWF JO DPME DPOEJUJPOT

r )PXFWFS
DBSCPIZESBUFT DBO CF EJHFTUFE NPSF FBTJMZ UIBO MJQJET
NBLJOH

DBSCPIZESBUF TUPSFT NPSF SFBEJMZ BWBJMBCMF TPVSDFT PG FOFSHZ

& :meaV^c l]n lViZg bV`Zh V \ddY XddaVci [dg Vc^bVah#

' HiViZ l]n \ajXdhZ ^h cdi jhZY Vh Vc ZcZg\n hidgV\Z bdaZXjaZ#

( 9^hi^c\j^h] WZilZZc ]nYgdanh^h VcY XdcYZchVi^dc gZVXi^dch#

(#( 9C6 higjXijgZ

6hhZhhbZci hiViZbZcih

r 0VUMJOF %/" OVDMFPUJEF TUSVDUVSF JO UFSNT PG TVHBS EFPYZSJCPTF

CBTF BOE QIPTQIBUF
r 4UBUF UIF OBNFT PG UIF GPVS CBTFT JO %/"
r 0VUMJOF IPX %/" OVDMFPUJEFT BSF MJOLFE UPHFUIFS CZ DPWBMFOU CPOET JOUP B TJOHMF TUSBOE
r &YQMBJO IPX B %/" EPVCMF IFMJY JT GPSNFE VTJOH DPNQMFNFOUBSZ CBTF QBJSJOH BOE IZESPHFO CPOET
r %SBX BOE MBCFM B TJNQMF EJBHSBN PG UIF NPMFDVMBS TUSVDUVSF PG %/"

)+

DNA EFPYZSJCPOVDMFJD BDJE
NPMFDVMFT NBLF VQ UIF HFOFUJD NBUFSJBM PG e]dhe]ViZ
MJWJOH PSHBOJTNT %/" JT BO FYUSFNFMZ MPOH NPMFDVMF CVU
MJLF QSPUFJOT

BOE DBSCPIZESBUFT
JU JT CVJMU VQ PG NBOZ TVCVOJUT 5IF TVCVOJUT PG %/"

BSF DBMMFE nucleotides

&BDI OVDMFPUJEF DPOTJTUT PG UISFF QBSUT m B TVHBS EFPYZSJCPTF

B

QIPTQIBUF HSPVQ BOE B OJUSPHFOPVT CBTF 'JHVSF 3.8
%/" DPOUBJOT GPVS

EJĄ FSFOU CBTFT BEFOJOF
HVBOJOF
DZUPTJOF BOE UIZNJOF 5IFTF BSF VTVBMMZ WVhZ

LOPXO CZ UIFJS MFUUFST "
(
$ BOE 5 'JHVSF 3.9
YZdmng^WdhZ

5P GPSN B %/" NPMFDVMF
OVDMFPUJEFT BSF MJOLFE UPHFUIFS 5IF ;^\jgZ (#- I]Z \ZcZgVa higjXijgZ d[ V 9C6
QIPTQIBUF HSPVQ PG POF OVDMFPUJEF MJOLT UP UIF EFPYZSJCPTF PG UIF cjXaZdi^YZ#

OFYU NPMFDVMF UP GPSN B DIBJO PG OVDMFPUJEFT
BT TIPXO JO 'JHVSF 3.10

PWFSMFBG
5IF TVHBS BOE QIPTQIBUF HSPVQT BSF JEFOUJDBM BMM UIF XBZ BMPOH

UIF DIBJO BOE GPSN UIF CBDLCPOF PG UIF %/" NPMFDVMF 5IF TFRVFODF PG

CBTFT JO UIF DIBJO XJMM WBSZ BOE JU JT UIJT TFRVFODF UIBU GPSNT UIF HFOFUJD

DPEF EFUFSNJOJOH UIF DIBSBDUFSJTUJDT PG BO PSHBOJTN

5XP TUSBOET PG OVDMFPUJEFT BSF MJOLFE CZ IZESPHFO CPOET UIBU GPSN

CFUXFFO UIF CBTFT BOE UIJT EPVCMF TUSBOE NBLFT VQ UIF EPVCMF IFeMJ]Yd hPe]G ViZ eZcidhZ dg\Vc^X
hj\Vg WVhZ
B DPNQMFUF %/" NPMFDVMF 'JHVSF 3.10
"EFOJOF BMXBZT QBJST XJUI

UIZNJOF BOE JT CPOEFE XJUI UXP IZESPHFO CPOET
XIJMF DZUPTJOF JT QBJSFE

XJUI HVBOJOF CZ UISFF IZESPHFO CPOET 5IF BSSBOHFNFOU JT LOPXO BT

complementary base pairing /PUJDF UIBU UIF UXP %/" DIBJOT SVO JO

PQQPTJUF EJSFDUJPOT BOE BSF TBJE UP CF antiparallel

:PV DBO JNBHJOF UIF NPMFDVMF SBUIFS MJLF B SPQF MBEEFS XJUI UIF TVHBSm I
QIPTQIBUF CBDLCPOF CFJOH UIF TJEFT PG UIF MBEEFS BOE UIF SVOHT CFJOH

GPSNFE CZ UIF IZESPHFO CPOEFE CBTF QBJST 5P GPSN UIFe nDgI^bB^SYB^DcZUFh SJTUJD i]nb^cZ
EPVCMF IFMJY PG B %/" NPMFDVMF
UIF MBEEFS NVTU CF UXJTUFE UP SFTFNCMF

B TQJSBM TUBJSDBTF

e]dhe]ViZ eZcidhZ dg\Vc^X 8
hj\Vg WVhZ Xnidh^cZ

eng^b^Y^cZh I ejg^cZh 6
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8 <
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ejg^cZh 6
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r &YQMBJO %/" SFQMJDBUJPO JO UFSNT PG VOXJOEJOH UIF EPVCMF IFMJY BOE TFQBSBUJPO PG UIF TUSBOET CZ IFMJDBTF
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r &YQMBJO UIF TJHOJê DBODF PG DPNQMFNFOUBSZ CBTF QBJSJOH JO UIF DPOTFSWBUJPO PG UIF CBTF TFRVFODF PG %/"
r 4UBUF UIBU %/" SFQMJDBUJPO JT TFNJ DPOTFSWBUJWF

"O FTTFOUJBM GFBUVSF PG %/" JT UIBU JU NVTU CF BCMF UP SFQMJDBUF JUTFMG
BDDVSBUFMZ
TP UIBU XIFO B DFMM EJWJEFT UIF HFOFUJD DPEF JU DBSSJFT DBO CF
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TP UIBU OFX NPMFDVMFT BSF QSPEVDFE XJUI FYBDUMZ UIF TBNF TFRVFODF PG
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EVSJOH UIF 4 QIBTF PG UIF JOUFSQIBTF PG UIF DFMM DZDMF XIFO %/" JT OPU
UJHIUMZ DPJMFE

"T 'JHVSF 3.11 TIPXT
UIJT QSPDFTT EPFT OPU PDDVS JO B IBQIB[BSE
NBOOFS "O FO[ZNF DBMMFE IFMJDBTF VO[JQT POF SFHJPO PG UIF %/"
NPMFDVMF BOE OVDMFPUJEFT BSF BEEFE JO B TUFQ CZ TUFQ QSPDFTT UIBU MJOLT
UIFN UP POF BOPUIFS BOE UP UIFJS DPNQMFNFOUBSZ CBTFT JO BO BSFB LOPXO
BT UIF SFQMJDBUJPO GPSL
1 5IF ê STU TUFQ JO UIF QSPDFTT JT UIF AVO[JQQJOH PG UIF UXP TUSBOET

)FMJDBTF NPWFT BMPOH UIF EPVCMF IFMJY
VOXJOEJOH UIF UXP TUSBOET

XIJDI TFQBSBUF GSPN POF BOPUIFS BT UIF SFMBUJWFMZ XFBL IZESPHFO CPOET
CFUXFFO UIF CBTFT BSF CSPLFO

)-

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2 5IF VOQBJSFE OVDMFPUJEFT BSF FYQPTFE BOE FBDI TJOHMF TUSBOE OPX BDUT
BT B UFNQMBUF GPS UIF GPSNBUJPO PG B OFX DPNQMFNFOUBSZ TUSBOE 'SFF
OVDMFPUJEFT NPWF JOUP QMBDF $ QBJST XJUI ( BOE " QBJST XJUI 5

3 5IF GSFF OVDMFPUJEF CBTFT GPSN DPNQMFNFOUBSZ QBJST XJUI UIF CBTFT
PO UIF TJOHMF %/" TUSBOET %/" QPMZNFSBTF JT UIF FO[ZNF JOWPMWFE
JO MJOLJOH UIF OFX OVDMFPUJEFT JOUP QMBDF 'JOBMMZ
UIF UXP OFX %/"
NPMFDVMFT BSF SFXPVOE
FBDI POF GPSNJOH B OFX EPVCMF IFMJY

5IF UXP OFX %/" TUSBOET UIBU BSF QSPEVDFE BSF BCTPMVUFMZ JEFOUJDBM UP
UIF PSJHJOBM TUSBOET $PNQMFNFOUBSZ CBTF QBJSJOH CFUXFFO UIF UFNQMBUF
TUSBOE BOE UIF OFX TUSBOE FOTVSFT UIBU BO BDDVSBUF DPQZ PG UIF PSJHJOBM
%/" JT NBEF FWFSZ UJNF SFQMJDBUJPO PDDVST %/" SFQMJDBUJPO JT TBJE UP CF
semi-conservative CFDBVTF OP %/" NPMFDVMF JT FWFS DPNQMFUFMZ OFX
&WFSZ EPVCMF IFMJY DPOUBJOT POF APSJHJOBM BOE POF AOFX TUSBOE

(#* IgVchXg^ei^dc VcY igVchaVi^dc

6hhZhhbZci hiViZbZcih

r $PNQBSF UIF TUSVDUVSF PG 3/" BOE %/"
r 0VUMJOF %/" USBOTDSJQUJPO JO UFSNT PG UIF GPSNBUJPO PG BO 3/" TUSBOE DPNQMFNFOUBSZ UP UIF %/" TUSBOE CZ

3/" QPMZNFSBTF

r %FTDSJCF UIF HFOFUJD DPEF JO UFSNT PG DPEPOT DPNQPTFE PG USJQMFUT PG CBTFT
r &YQMBJO UIF QSPDFTT PG USBOTMBUJPO MFBEJOH UP QPMZQFQUJEF GPSNBUJPO
r %JTDVTT UIF SFMBUJPOTIJQ CFUXFFO POF HFOF BOE POF QPMZQFQUJEF

( I=: 8=:B>HIGN D; A>;: ).

5IF NBJO SPMF PG %/" JT UP EJSFDU UIF BDUJWJUJFT PG UIF DFMM *U EPFT UIJT
CZ DPOUSPMMJOH UIF QSPUFJOT UIBU UIF DFMM QSPEVDFT &O[ZNFT
IPSNPOFT
BOE NBOZ PUIFS JNQPSUBOU CJPDIFNJDBM NPMFDVMFT BSF QSPUFJOT
XIJDI
DPOUSPM XIBU UIF DFMM CFDPNFT
XIBU JU TZOUIFTJTFT BOE IPX JU GVODUJPOT
1SPUFJO TZOUIFTJT DBO CF EJWJEFE JOUP UXP TFUT PG SFBDUJPOT UIF ê STU JT
transcription BOE UIF TFDPOE
translation *O FVLBSZPUFT
USBOTDSJQUJPO
PDDVST JO UIF OVDMFVT BOE USBOTMBUJPO JO UIF DZUPQMBTN

5IF TFDUJPOT PG %/" UIBU DPEF GPS QBSUJDVMBS QSPUFJOT BSF LOPXO BT
genes (FOFT DPOUBJO TQFDJê D TFRVFODFT PG CBTFT JO TFUT PG UISFF
DBMMFE
triplets 4PNF USJQMFUT DPOUSPM XIFSF USBOTDSJQUJPO CFHJOT BOE FOET

IgVchXg^ei^dc

5IF ê STU TUBHF JO UIF TZOUIFTJT PG B QSPUFJO JT UIF QSPEVDUJPO PG BO
JOUFSNFEJBUF NPMFDVMF UIBU DBSSJFT UIF DPEFE NFTTBHF PG %/" JOUP UIF
DZUPQMBTN XIFSF UIF QSPUFJO DBO CF QSPEVDFE 5IJT JOUFSNFEJBUF NPMFDVMF
JT DBMMFE messenger RNA PS mRNA 3/" SJCPOVDMFJD BDJE
IBT
TJNJMBSJUJFT BOE EJĄ FSFODFT XJUI %/" BOE UIFTF BSF TIPXO JO 5BCMF 3.4

9C6 GC6

XdciV^ch i]Z *"XVgWdc hj\Vg YZdmng^WdhZ XdciV^ch i]Z *"XVgWdc hj\Vg g^WdhZ
XdciV^ch i]Z WVhZh VYZc^cZ! \jVc^cZ! Xnidh^cZ VcY i]nb^cZ
XdciV^ch i]Z WVhZh VYZc^cZ! \jVc^cZ! Xnidh^cZ VcY jgVX^a
V YdjWaZ"higVcYZY bdaZXjaZ ^chiZVY d[ i]nb^cZ

V h^c\aZ"higVcYZY bdaZXjaZ

IVWaZ (#) 8dbeVg^c\ 9C6 VcY GC6#

5IF CVJMEJOH CMPDLT GPS 3/" BSF UIF 3/" OVDMFPUJEFT UIBU BSF GPVOE
JO UIF OVDMFVT $PNQMFNFOUBSZ CBTF QBJSJOH PG 3/" UP %/" PDDVST
JO FYBDUMZ UIF TBNF XBZ BT JO UIF SFQMJDBUJPO QSPDFTT CVU UIJT UJNF VSBDJM
6
QBJST XJUI BEFOJOF TJODF UIFSF JT OP UIZNJOF 5
GPVOE JO 3/"
5SBOTDSJQUJPO SFTVMUT JO UIF DPQZJOH PG POF TFDUJPO PG UIF %/" NPMFDVMF

OPU JUT FOUJSF MFOHUI 'JHVSF 3.12 EFTDSJCFT UIF QSPDFTT

& ]nYgd\Zc WdcYh
WZilZZc WVhZ eV^gh
Wgd`Zc " Èjco^ee^c\É

' [gZZ cjXaZdi^YZh ( WVhZ eV^g^c\ gZVXi^dch [dgb Vc bGC6 higVcY
Y^[[jhZ ^cid edh^i^dc Ä i]Z gZ[ZgZcXZ higVcY d[ i]Z 9C6 VXih Vh V iZbeaViZ

bGC6
higVcY

gZ[ZgZcXZ
higVcY d[ 9C6

;^\jgZ (#&' IgVchXg^ei^dc#
*%

1 %/" JT VO[JQQFE CZ UIF FO[ZNF 3/" QPMZNFSBTF
BOE UIF UXP 5IF N3/" DPEPOT UIBU DPEF GPS
TUSBOET VODPJM BOE TFQBSBUF FBDI BNJOP BDJE BSF TIPXO JO
5BCMF 4.1 PO QBHF 68
2 'SFF OVDMFPUJEFT NPWF JOUP QMBDF BMPOH POF PG UIF UXP TUSBOET
3 5IF TBNF FO[ZNF
3/" QPMZNFSBTF
BTTFNCMFT UIF GSFF OVDMFPUJEFT 5SBOTGFS 3/" U3/"
JT B TJOHMF
TUSBOE PG 3/" UIBU JT GPMEFE JOUP
JO UIF DPSSFDU QMBDFT VTJOH DPNQMFNFOUBSZ CBTF QBJSJOH "T UIF 3/" B ADMPWFS MFBG TIBQF 'JHVSF 3.14

OVDMFPUJEFT BSF MJOLFE UPHFUIFS
B TJOHMF TUSBOE PG N3/" JT GPSNFE QBHF 53
8JUIJO UIF NPMFDVMF

5IJT NPMFDVMF JT NVDI TIPSUFS UIBO UIF %/" NPMFDVMF CFDBVTF JU JT B TFDUJPOT BSF CPOEFE UPHFUIFS CZ
DPQZ PG KVTU POF TFDUJPO m B HFOF 5IF N3/" TFQBSBUFT GSPN UIF %/" DPNQMFNFOUBSZ CBTF QBJSJOH CVU
BOE UIF %/" EPVCMF IFMJY JT [JQQFE VQ BHBJO CZ 3/" QPMZNFSBTF POF QBSUJDVMBS BSFB JT FYQPTFE
0ODF BO N3/" NPMFDVMF IBT CFFO USBOTDSJCFE
JU NPWFT WJB UIF QPSFT JO UP SFWFBM B USJQMFU PG CBTFT DBMMFE
UIF OVDMFBS FOWFMPQF UP UIF DZUPQMBTN XIFSF UIF QSPDFTT PG USBOTMBUJPO DBO BO anticodon 5IJT USJQMFU
UBLF QMBDF DPSSFTQPOET UP POF PG UIF DPEPOT
GPVOE JO N3/" "U UIF PQQPTJUF
IgVchaVi^dc FOE PG UIF U3/" NPMFDVMF JT B
CJOEJOH TJUF GPS POF BNJOP BDJE

%VF UP DPNQMFNFOUBSZ CBTF QBJSJOH
UIF TFRVFODF PG CBTFT BMPOH UIF XIJDI DPSSFTQPOET UP UIF DPEPO
N3/" NPMFDVMF DPSSFTQPOET UP UIF TFRVFODF PO UIF PSJHJOBM %/" PO N3/" UIBU NBUDIFT UIF
NPMFDVMF &BDI TFRVFODF PG UISFF CBTFT
DBMMFE B USJQMFU
DPSSFTQPOET UP B BOUJDPEPO PG UIF U3/"
TQFDJê D BNJOP BDJE
TP UIF PSEFS PG UIFTF USJQMFUT EFUFSNJOFT IPX BNJOP
BDJET XJMM CF BTTFNCMFE JOUP QPMZQFQUJEF DIBJOT JO UIF DZUPQMBTN ( I=: 8=:B>HIGN D; A>;: *&

5SBOTMBUJPO JT UIF QSPDFTT CZ XIJDI UIF DPEFE JOGPSNBUJPO JO N3/"
TUSBOET JT VTFE UP DPOTUSVDU QPMZQFQUJEF DIBJOT
XIJDI JO UVSO NBLF
GVODUJPOJOH QSPUFJOT &BDI USJQMFU PG N3/" CBTFT JT DBMMFE B codon BOE
DPEFT GPS POF BNJOP BDJE 5SBOTMBUJPO JT DBSSJFE PVU JO UIF DZUPQMBTN CZ
TUSVDUVSFT DBMMFE ribosomes 'JHVSF 3.13
PWFSMFBG
BOE NPMFDVMFT PG
BOPUIFS UZQF PG 3/" LOPXO BT transfer RNA PS tRNA 'JHVSF 3.14

QBHF 53


3JCPTPNFT IBWF CJOEJOH TJUFT GPS CPUI UIF N3/" NPMFDVMF BOE U3/"
NPMFDVMFT 5IF SJCPTPNF CJOET UP UIF N3/" BOE UIFO ESBXT JO TQFDJê D
U3/" NPMFDVMFT XJUI anticodons UIBU NBUDI UIF N3/" DPEPOT

0OMZ UXP U3/" NPMFDVMFT CJOE UP UIF SJCPTPNF BU PODF &BDI POF
DBSSJFT XJUI JU UIF BNJOP BDJE TQFDJê FE CZ JUT BOUJDPEPO 5IF BOUJDPEPO PG
UIF U3/" CJOET UP UIF DPNQMFNFOUBSZ DPEPO PG UIF N3/" NPMFDVMF
XJUI IZESPHFO CPOET

8IFO UXP U3/" NPMFDVMFT BSF JO QMBDF PO UIF SJCPTPNF
B peptide
bond GPSNT CFUXFFO UIF UXP BNJOP BDJET UIFZ DBSSZ UP GPSN B EJQFQUJEF
0ODF B EJQFQUJEF IBT CFFO GPSNFE
UIF ê STU U3/" NPMFDVMF EFUBDIFT
GSPN CPUI UIF BNJOP BDJE BOE UIF SJCPTPNF 5IF SJCPTPNF NPWFT BMPOH
UIF N3/" POF USJQMFU UP UIF OFYU DPEPO

5IFTF QSPDFTTFT
TIPXO JO 'JHVSF 3.13 PWFSMFBG
BSF SFQFBUFE PWFS BOE
PWFS BHBJO VOUJM UIF DPNQMFUF QPMZQFQUJEF JT GPSNFE 5IF ê OBM DPEPO
UIBU JT SFBDIFE JT B ATUPQ DPEPO
XIJDI EPFT OPU DPEF GPS BO BNJOP BDJE
CVU UFMMT UIF SJCPTPNF UP EFUBDI GSPN UIF N3/" "T JU EPFT TP
UIF
QPMZQFQUJEF ë PBUT GSFF JO UIF DZUPQMBTN

ÈDcZ \ZcZ! dcZ edaneZei^YZÉ ]nedi]Zh^h

*O UIF T
TDJFOUJTUT QSPQPTFE UIBU FBDI HFOF XBT SFTQPOTJCMF GPS UIF
QSPEVDUJPO PG POF QSPUFJO -BUFS
UIF IZQPUIFTJT XBT NPEJê FE UP TUBUF UIBU

i]Z \ZcZi^X XdYZ ^c eVgi d[ Vc bGC6 bdaZXjaZ
i]Z bGC6 bdaZXjaZ ^h gZVY ^c i]^h Y^gZXi^dc

i]Z \ZcZi^X XdYZ ^c i]Z bGC6 bdaZXjaZ

I]^h XdYdc gZegZhZcih I]^h XdYdc gZegZhZcih I]^h XdYdc gZegZhZcih I]^h XdYdc gZegZhZcih I]^h XdYdc gZegZhZcih
i]Z Vb^cd VX^Y i]Z Vb^cd VX^Y i]Z Vb^cd VX^Y hZg^cZ# i]Z Vb^cd VX^Y ÈZcYÉ0 ÈhideÉ XdYdc#
bZi]^dc^cZ0 ÈhiVgiÉ VheVgiViZ# XnhiZ^cZ#
XdYdc#

IgVchaVi^dc dc V g^WdhdbZ BZi 6he

& 8dbeaZbZciVgn ' 6cdi]Zg Vb^cd
WVhZ eV^g^c\ VX^Y ^h Wgdj\]i
WZilZZc XdYdc ^c ViiVX]ZY id
VcY Vci^XdYdc# ^ih iGC6#

BZi 6he ( 6 XdcYZchVi^dc
gZVXi^dc [dgbh V
eZei^YZ WdcY#

) I]Z g^WdhdbZ bdkZh Vadc\ i]Z bGC6
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BZi 6he HZg

* 6cdi]Zg Vb^cd
VX^Y ^h Wgdj\]i ^c#

;^\jgZ (#&( IgVchaVi^dc#

*'

POF HFOF QSPEVDFT POF QPMZQFQUJEF
XIFO JU XBT EJTDPWFSFE UIBU TPNF ed^ci d[ ViiVX]bZci
QSPUFJOT BSF DPNQPTFE PG NPSF UIBO POF QPMZQFQUJEF TVCVOJU BOE UIBU d[ Vb^cd VX^Y
FBDI TVCVOJU JT DPEFE GPS CZ JUT PXO TQFDJê D HFOF "O FYBNQMF PG UIJT JT
IFNPHMPCJO
XIJDI JT DPNQPTFE PG UXP QBJST PG TVCVOJUT BOE JT DPEFE GPS cjXaZdi^YZh
CZ UXP HFOFT
]nYgd\Zc
5PEBZ
JU JT HFOFSBMMZ BHSFFE UIBU FBDI HFOF EPFT DPEF GPS B TJOHMF WdcYh
QPMZQFQUJEF
CVU UIBU UIFSF BSF TPNF FYDFQUJPOT UP UIF SVMF 'PS FYBNQMF

TPNF %/" TFRVFODFT BDU BT SFHVMBUPST GPS UIF FYQSFTTJPO PG PUIFS HFOFT i]Z Vci^XdYdc
BOE BSF OPU USBOTDSJCFE PS USBOTMBUFE UIFNTFMWFT 0UIFST DPEF GPS N3/"
PS U3/" CVU OPU GPS QSPUFJOT .PTU SFDFOUMZ
SFTFBSDIFST IBWF GPVOE UIBU I]^h iGC6 ^h a^c`ZY
TPNF HFOFT DPEF GPS TJOHMF N3/" TUSBOET XIJDI BSF UIFO NPEJê FE JO
UIF DZUPQMBTN 7BSJBUJPOT JO UIF NPEJê DBUJPOT DBO MFBE UP UIF QSPEVDUJPO id bZi]^dc^cZ# BZi
PG EJĄ FSFOU QPMZQFQUJEFT XIFO UIF N3/" JT USBOTMBUFE 'PS FYBNQMF

XIFO BOUJCPEJFT BSF QSPEVDFE
MZNQIPDZUFT TQMJDF UPHFUIFS TFDUJPOT PG
3/" JO EJĄ FSFOU XBZT UP NBLF B SBOHF PG BOUJCPEZ QSPUFJOT *O B GFX
DFMMT
UIFSF JT EJĄ FSFOUJBM FYQSFTTJPO PG DFSUBJO HFOFT
JOë VFODFE CZ UIF
UZQF PG UJTTVF JO XIJDI UIF DFMMT BSF GPVOE 0OF FYBNQMF PG UIJT JT UIF
FYQSFTTJPO PG HFOFT UIBU QSPEVDF UIF JOTVMJO MJLF HSPXUI GBDUPST *('
BOE *('
JO UIF MJWFS

) 9gVl VcY aVWZa V cjXaZdi^YZ# I]Z Vci^XdYdc dc i]^h iGC6 ^h J68#
* L]ZgZ ^c V XZaa YdZh igVchaVi^dc iV`Z eaVXZ4
+ A^hi i]Z Y^[[ZgZcXZh WZilZZc 9C6 VcY GC6# ;^\jgZ (#&) I]Z higjXijgZ d[ V iGC6
, L]Vi ^h XdbeaZbZciVgn WVhZ eV^g^c\4 bdaZXjaZ#

(#+ :conbZh

6hhZhhbZci hiViZbZcih

r %Fê OF AFO[ZNF BOE ABDUJWF TJUF
r &YQMBJO FO[ZNFmTVCTUSBUF TQFDJê DJUZ
r &YQMBJO UIF FĄ FDUT PG UFNQFSBUVSF
Q) BOE TVCTUSBUF DPODFOUSBUJPO PO FO[ZNF BDUJWJUZ
r %Fê OF AEFOBUVSBUJPO
r &YQMBJO UIF VTF PG MBDUBTF JO UIF QSPEVDUJPO PG MBDUPTF GSFF NJML

:conbZh VcY VXi^kZ h^iZh

"O enzyme JT B CJPMPHJDBM catalyst $BUBMZTUT TQFFE VQ CJPDIFNJDBM
SFBDUJPOT
TVDI BT EJHFTUJPO BOE SFTQJSBUJPO
CVU UIFZ SFNBJO VODIBOHFE
BU UIF FOE PG UIF QSPDFTT "MM FO[ZNFT BSF QSPUFJOT XJUI MPOH QPMZQFQUJEF
DIBJOT UIBU BSF GPMEFE JOUP UISFF EJNFOTJPOBM TIBQFT 5IF BSSBOHFNFOU PG
UIFTF TIBQFT JT WFSZ QSFDJTF BOE HJWFT FBDI FO[ZNF UIF BCJMJUZ UP DBUBMZTF
POF TQFDJê D SFBDUJPO *G UIF UISFF EJNFOTJPOBM TIBQF PG BO FO[ZNF JT
EFTUSPZFE PS EBNBHFE
JU DBO OP MPOHFS DBSSZ PVU JUT KPC BOE JT TBJE UP CF

( I=: 8=:B>HIGN D; A>;: *(

Enzyme B HMPCVMBS QSPUFJO UIBU denatured &YUSFNFT PG UFNQFSBUVSF
IFBWZ NFUBMT BOE
JO TPNF DBTFT
Q)
GVODUJPOT BT B CJPMPHJDBM DBUBMZTU PG DBO DBVTF QFSNBOFOU DIBOHFT JO BO FO[ZNF
DIFNJDBM SFBDUJPOT
Denaturation JSSFWFSTJCMF DIBOHFT 5IF UISFF EJNFOTJPOBM TIBQF PG BO FO[ZNF JT DSVDJBM UP UIF XBZ JU
UP UIF TUSVDUVSF PG BO FO[ZNF PS XPSLT *O UIF TUSVDUVSF PG FWFSZ FO[ZNF JT B TQFDJBMMZ TIBQFE SFHJPO
PUIFS QSPUFJO TP UIBU JU DBO OP LOPXO BT BO active site 'JHVSF 3.15
*U JT IFSF UIBU UIF TVCTUSBUFT BSF
MPOHFS GVODUJPO CSPVHIU UPHFUIFS 5IF TVCTUSBUFT BSF UIF DIFNJDBMT JOWPMWFE JO UIF SFBDUJPO
Active site SFHJPO PO UIF TVSGBDF DBUBMZTFE CZ UIF FO[ZNF 5IF TIBQFT PG UIF FO[ZNF BOE TVCTUSBUFT BSF
PG BO FO[ZNF NPMFDVMF XIFSF B DPNQMFNFOUBSZ
TP UIBU UIFZ ê U UPHFUIFS QFSGFDUMZ MJLF B LFZ ê UT JOUP B MPDL
TVCTUSBUF NPMFDVMF CJOET BOE XIJDI 5IF AMPDL BOE LFZ IZQPUIFTJT JT B XBZ PG FYQMBJOJOH IPX FBDI FO[ZNF DBO
DBUBMZTFT B SFBDUJPO JOWPMWJOH UIF CF TP TQFDJê D 5P VOMPDL B EPPS SFRVJSFT KVTU POF TQFDJBM LFZ 5P DBUBMZTF B
TVCTUSBUFT SFBDUJPO SFRVJSFT POF TQFDJBM FO[ZNF +VTU BT POMZ POF LFZ ê UT QFSGFDUMZ JOUP
UIF MPDL
POMZ POF TVCTUSBUF ê UT QFSGFDUMZ JOUP UIF BDUJWF TJUF PG BO FO[ZNF

0ODF JO QMBDF JO BO BDUJWF TJUF
TVCTUSBUFT NBZ CF CPOEFE UPHFUIFS UP GPSN
B OFX TVCTUBODF PS UIFZ NBZ CF CSPLFO BQBSU JO QSPDFTTFT TVDI BT EJHFTUJPO
BOE SFTQJSBUJPO 'PS FYBNQMF
POF UZQF PG FO[ZNF CPOET BNJOP BDJET
UPHFUIFS UP GPSN B QPMZQFQUJEF
XIJMF WFSZ EJĄ FSFOU FO[ZNFT BSF JOWPMWFE JO
EJHFTUJOH UIFN

;VXidgh V[[ZXi^c\ ZconbZ VXi^dc

&O[ZNFT XPSL JO NBOZ EJĄ FSFOU QMBDFT JO MJWJOH PSHBOJTNT BOE UIFZ
SFRVJSF TQFDJBM DPOEJUJPOT UP XPSL BU UIFJS HSFBUFTU
PS PQUJNVN
Fą DJFODZ
5FNQFSBUVSF
Q) BOE UIF DPODFOUSBUJPO PG UIF TVCTUSBUFT JOWPMWFE BMM BĄ FDU
UIF SBUF BU XIJDI FO[ZNFT PQFSBUF BOE QSPEVDF UIFJS QSPEVDUT

hjWhigViZ ZconbZÄhjWhigViZ XdbeaZm egdYjXih

VXi^kZ h^iZ

ZconbZ W GVcYdb bdkZbZci d[ X I]Z ^ciZgVXi^dc d[ i]Z
ZconbZ VcY hjWhigViZ Wg^c\h hjWhigViZ l^i] i]Z VXi^kZ h^iZ
V 6c ZconbZ ]Vh V XaZ[i ^c ^ih i]Z hjWhigViZ ^cid i]Z VXi^kZ WgZV`h i]Z hjWhigViZ VeVgi# I]Z
hjg[VXZ XVaaZY i]Z VXi^kZ h^iZ# h^iZ# 6c ZconbZÄhjWhigViZ ild egdYjXi bdaZXjaZh aZVkZ i]Z
I]Z hjWhigViZ bdaZXjaZ ]Vh V XdbeaZm ^h iZbedgVg^an [dgbZY# VXi^kZ h^iZ! aZVk^c\ i]Z ZconbZ
XdbeaZbZciVgn h]VeZ# I]Z G \gdjeh d[ i]Z Vb^cd bdaZXjaZ jcX]Vc\ZY VcY gZVYn
VX^Yh ^c i]Z VXi^kZ h^iZ ^ciZgVXi id W^cY l^i] Vcdi]Zg hjWhigViZ
l^i] i]Z hjWhigViZ# bdaZXjaZ#

ZconbZ hjWhigViZ ZconbZ

ZconbZÄhjWhigViZ egdYjXih
XdbeaZm

VXi^kZ h^iZ

;^\jgZ (#&* =dl Vc ZconbZ XViVanhZh i]Z WgZV`Ydlc d[ V hjWhigViZ bdaZXjaZ ^cid ild egdYjXi bdaZXjaZh#
*)

IZbeZgVijgZ

&O[ZNFT BOE UIFJS TVCTUSBUFT VTVBMMZ NFFU BT B SFTVMU PG SBOEPN DPMMJTJPOT
CFUXFFO UIFJS NPMFDVMFT
XIJDI ë PBU GSFF JO CPEZ ë VJET PS DZUPQMBTN *O UIF
IVNBO CPEZ
NPTU SFBDUJPOT QSPDFFE BU UIFJS HSFBUFTU SBUF BU B UFNQFSBUVSF
PG BCPVU ž$ BOE EFWJBUJPOT GSPN UIJT optimum temperature BĄ FDU UIF
SFBDUJPO SBUF
BT UIF HSBQI JO 'JHVSF 3.16 TIPXT

GViZ d[ gZVXi^dc

% &% '% (% )% *% +% ,%
IZbeZgVijgZ $ •8

;^\jgZ (#&+ I]Z Z[[ZXi d[ iZbeZgVijgZ dc i]Z gViZ d[ Vc ZconbZ"XdcigdaaZY gZVXi^dc#
6c ZconbZ ldg`h bdhi Z[Ò X^Zcian Vi ^ih dei^bjb iZbeZgVijgZ#

#FMPX ž$
NPMFDVMFT JO TPMVUJPO NPWF NPSF TMPXMZ TP UIF MJLFMJIPPE
PG DPMMJTJPO CFUXFFO UIFN JT SFEVDFE 5IJT TMPXT EPXO UIF QSPEVDUJPO PG
QSPEVDUT "U WFSZ MPX UFNQFSBUVSFT
FO[ZNFT IBSEMZ XPSL BU BMM BOE UIF
SBUF PG SFBDUJPO JT WFSZ MPX "T UIF UFNQFSBUVSF SJTFT
NPMFDVMBS DPMMJTJPOT
BSF NPSF GSFRVFOU BOE FOFSHFUJD
BOE UIFSFGPSF UIF SBUF PG UIF FO[ZNF
DPOUSPMMFE SFBDUJPO JODSFBTFT

"T UIF UFNQFSBUVSF SJTFT BCPWF UIF PQUJNVN
UIF FO[ZNF BOE TVCTUSBUF
NPMFDVMFT NPWF GBTUFS m CVU BUPNT XJUIJO UIF FO[ZNF NPMFDVMF JUTFMG
BMTP NPWF GBTUFS
TUSBJOJOH UIF CPOET IPMEJOH JU UPHFUIFS &WFOUVBMMZ
UIFTF
CPOET NBZ CF TUSFTTFE PS CSPLFO UP TVDI BO FYUFOU UIBU UIF FO[ZNF
MPTFT JUT UISFF EJNFOTJPOBM TIBQF BOE UIF BDUJWF TJUF DBO OP MPOHFS
SFDFJWF TVCTUSBUF NPMFDVMFT "U UIFTF IJHI UFNQFSBUVSFT
UIF TUSVDUVSF JT
QFSNBOFOUMZ EFTUSPZFE BOE UIF FO[ZNF JT EFOBUVSFE BOE DBO OP MPOHFS
DBUBMZTF UIF SFBDUJPO

e=
Q) JT B NFBTVSF PG UIF SFMBUJWF OVNCFST PG ) BOE 0)− JPOT JO B
TPMVUJPO " TPMVUJPO XJUI B MPX Q) WBMVF IBT NBOZ GSFF ) JPOT BOE JT
BDJEJD
XIFSFBT B IJHI Q) WBMVF JOEJDBUFT NPSF 0)− JPOT BOE B CBTJD
TPMVUJPO 1VSF XBUFS JT OFVUSBM BOE IBT B Q) WBMVF PG JOEJDBUJOH UIBU UIF
OVNCFS PG 0)− BOE ) JPOT JT FRVBM

&O[ZNF BDUJPO JT JOë VFODFE CZ Q) CFDBVTF UIF BNJOP BDJET UIBU NBLF
VQ BO FO[ZNF NPMFDVMF DPOUBJO NBOZ QPTJUJWF BOE OFHBUJWF SFHJPOT
TPNF

( I=: 8=:B>HIGN D; A>;: **

PG XIJDI BSF BSPVOE UIF BDUJWF TJUF "O FYDFTT PG ) JPOT JO BO BDJEJD
TPMVUJPO DBO MFBE UP CPOEJOH CFUXFFO UIF ) JPOT BOE OFHBUJWF DIBSHFT JO
UIF BDUJWF TJUF PS PUIFS QBSUT PG UIF FO[ZNF 5IFTF JOUFSBDUJPOT DBO JOIJCJU
UIF NBUDIJOH QSPDFTT CFUXFFO UIF FO[ZNF BOE JUT TVCTUSBUF
BOE TMPX EPXO
PS FWFO QSFWFOU FO[ZNF BDUJWJUZ " TJNJMBS FĄ FDU PDDVST JG B TPMVUJPO CFDPNFT
UPP CBTJD m UIF FYDFTT PG OFHBUJWF JPOT VQTFUT UIF FO[ZNF JO UIF TBNF XBZ "U
FYUSFNFT PG Q)
UIF FO[ZNF NBZ FWFO MPTF JUT TIBQF BOE CF EFOBUVSFE

/PU BMM FO[ZNFT IBWF UIF TBNF optimum pH 1SPUFBTFT QSPUFJO
EJHFTUJOH FO[ZNFT
JO UIF TUPNBDI IBWF BO PQUJNVN Q) PG BOE XPSL
XFMM JO UIF BDJEJD DPOEJUJPOT UIFSF
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Chimpanzees are set apart from all other organisms because their parents were chimpanzees and
their offspring will also be chimpanzees.The study of genetics attempts to explain this process
of heredity and it also plays a very significant role in the modern world, from plant and animal
breeding to human health and disease.

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bjiVi^dc

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r State that eukaryotic chromosomes are made of DNA and proteins.
r Define ‘gene’,‘allele’ and ‘genome’.
r Define ‘gene mutation’.
r Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation,

using the example of sickle-cell anemia.

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During the phase of the cell cycle known as interphase, chromosomes eg^dg id XZaa Y^k^h^dc VcY hd Xdch^hi d[ ild
are in the form of long, very thin threads, which cannot be seen with ^YZci^XVa higVcYh X]gdbVi^Yh a^c`ZY Vi i]Z
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undergo repeated coiling and become much shorter and thicker
(Figure 4.1).When stained, they are clearly visible even at low microscope ) <:C:I>8H & +,
magnifications.

Eukaryotic cells contain chromosomes surrounded by a nuclear
envelope.The chromosomes of eukaryotic cells are associated with
proteins. Each chromosome contains a single molecule of DNA along
with these associated proteins. Some of these proteins are structural and
others regulate the activities of the DNA.

Chromosome structure is described in greater detail in Chapter 7.

8]gdbdhdbZh! \ZcZh VcY bjiVi^dch

A DNA molecule comprises a pair of strands, each strand consisting of a
linear sequence of nucleotides, held together by weak bonds between the
bases.This linear sequence of bases contains the genetic code in the form of
triplets of bases.A gene is a particular section of a DNA strand that, when
transcribed and translated, forms a specific polypeptide. (Transcription and
translation are described in Chapter 3 and in more detail in Chapter 7.)

8 6< 9C6 ig^eaZi A triplet of bases in the DNA molecule is transcribed into a triplet
<I8 of bases in the mRNA molecule, which is then translated into a specific
amino acid, as shown in Figure 4.2.
igVchXg^ei^dc
The process of DNA replication is complex and mistakes sometimes
8 6< GC6 ig^eaZi occur – a nucleotide may be left out, an extra one may be added, or
the wrong one inserted.These mistakes are known as gene mutations.
igVchaVi^dc The insertion of an incorrect nucleotide is called a base substitution
mutation. When the DNA containing an incorrect nucleotide is
\ajiVb^cZ Vb^cd VX^Y transcribed and translated, errors may occur in the polypeptide produced.

;^\jgZ )#' I]Z WVhZ hZfjZcXZ ^c 9C6 ^h Table 4.1 shows the amino acids that are specified by different mRNA
YZXdYZY k^V igVchXg^ei^dc VcY igVchaVi^dc# codons. Most amino acids are coded for by more than one codon and so
many substitution mutations have no effect on the final polypeptide that
Gene a heritable factor is produced. For example, a mutation in the DNA triplet CCA into CCG
that controls a specific would change the codon in the mRNA from GGU to GGC but it would
characteristic, or a section still result in the amino acid glycine being placed in a polypeptide. Some
of DNA that codes for the substitution mutations, however, do have serious effects and an important
formation of a polypeptide human condition that results from a single base substitution is sickle-cell
Allele a specific form of a anemia.
gene occupying the same
gene locus or position HZXdcY WVhZ
(page 77) as other alleles
of that gene, but differing J 86 <
from other alleles by small
differences in its base JJJ J8J J6J J<J J
sequence e]ZcnaVaVc^cZ ingdh^cZ XnhiZ^cZ 8
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the genetic information of JJ8 J88 J68 J<8
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change in the sequence of JJ6 J86 ÈhideÉ
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Sickle-cell anemia is a blood disorder in which red blood cells become
sickle shaped and cannot carry oxygen properly (Figure 4.3). It occurs
most frequently in people with African ancestry – about 1% suffer from
the condition and between 10% and 40% are carriers of it. Sickle-cell
anemia is due to a single base substitution mutation in one of the genes
that make hemoglobin, the oxygen-carrying pigment in red blood cells.

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;^\jgZ )#) I]Z higjXijgZ d[ V ]Zbd\adW^c bdaZXjaZ h]dl^c\ i]Z i]gZZ"Y^bZch^dcVa Only one strand of DNA is
VggVc\ZbZci d[ i]Z hjWjc^ih i]Vi bV`Z ^i je# transcribed into mRNA for any
gene.The transcribed strand is
Hemoglobin is made up of four subunits, as shown in Figure 4.4 – two called the coding strand.
B-chains and two C-chains.The 9 C-chains are affected by the sickle-cell
mutation.To form a normal C-chain, the particular triplet base pairing in ) <:C:I>8H & +.
the DNA is:

<6<

8I8

The C–T–C on the coding strand of the DNA is transcribed into the
mRNA triplet G–A–G, which in turn is translated to give glutamic acid
in the polypeptide chain of the C-subunit.

If the sickle-cell mutation occurs, the adenine base A is substituted for
thymine T on the coding strand, so the triplet base pairing becomes:

<I<

868

C–A–C on the coding strand of the DNA is now transcribed into the
mRNA triplet G–U–G, which in turn is translated to give the amino acid
valine.Valine replaces glutamic acid in the C-chain.

Valine has different properties from glutamic acid and so this single
change in the amino acid sequence has very serious effects.The resulting
hemoglobin molecule is a different shape, it is less soluble and when in
low oxygen concentrations, it deforms the red blood cells to give them a
sickle shape. Sickle cells carry less oxygen, which results in anemia.They
are also rapidly removed from the circulation, leading to a lack of red
blood cells and other symptoms such as jaundice, kidney problems and
enlargement of the spleen.

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h^X`aZ"XZaa VcZb^V! l]Vi ]Vh i]^h ig^eaZi bjiViZY id4
W 7ZXVjhZ d[ i]^h bjiVi^dc! dcZ Vb^cd VX^Y ^c i]Z edaneZei^YZ X]V^c d[
i]Z C"hjWjc^ih ^c ]Zbd\adW^c ^h VWcdgbVa# CVbZ i]Z cdgbVa Vb^cd
VX^Y VcY Vahd i]Z Vb^cd VX^Y gZhjai^c\ [gdb i]Z h^X`aZ"XZaa bjiVi^dc#
X :meaV^c l]n i]^h bjiVi^dc aZVYh id h^X`aZ"XZaa VcZb^V#
+ I]Z [daadl^c\ ^h V hZfjZcXZ d[ WVhZh ^c V 9C6 bdaZXjaZ i]Vi ]Vh WZZc
igVchXg^WZY ^cid Vc GC6 bdaZXjaZ#
8<<I66<88I6
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6 8<<I66<88I6
7 <886II<<6I
8 8<<J66<88J6
9 <88JII8<<6J

,%

)#' BZ^dh^h

6hhZhhbZci hiViZbZcih

r State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei.
r Define ‘homologous chromosomes’.
r Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two

divisions, which results in four haploid cells.

r Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down’s

syndrome (trisomy 21).

r State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure.
r State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for prenatal

diagnosis of chromosome abnormalities.

r Analyse a human karyotype to determine gender and whether non-disjunction has occurred.

BZ^dh^h ^h V gZYjXi^dc Y^k^h^dc Homologous chromosomes
a pair of chromosomes with the
Meiosis is a type of cell division that produces gametes (sex cells). In same genes but not necessarily the
any organism, each cell that is produced as a result of meiosis has half the same alleles of those genes
number of chromosomes of other cells in the body. There are a few organisms that
are haploid, for example the male
Eukaryotic body cells have a diploid nucleus, which contains two honey bee, Apis mellifera.This
copies of each chromosome, in homologous pairs. For example, humans means it produces gametes through
have a diploid number of 46 chromosomes in 23 pairs, mangos and mitosis.
soybean both have 40 chromosomes in 20 pairs, and the camel has 70
chromosomes in 35 pairs. ) <:C:I>8H & ,&

During sexual reproduction, two gametes fuse together so, in order to
keep the chromosome number correct in the offspring that are produced,
each gamete must contain only one of each chromosome pair.That is, it
must contain half the diploid number of chromosomes, which is called the
haploid number. During gamete formation, meiosis reduces the diploid
number to the haploid number.At the moment of fertilisation, the normal
diploid number is restored as the gametes fuse.

So, in the camel, the haploid sperm (35 chromosomes) and haploid egg
(35 chromosomes) fuse at fertilisation to form the diploid zygote, with 70
chromosomes.

I]Z egdXZhh d[ bZ^dh^h

Meiosis occurs in a series of stages, as illustrated in Figure 4.5 (overleaf),
which result in the production of four cells.

Whereas mitosis, used to replace or repair cells, is achieved with
one cell division, meiosis involves two divisions – the first reduces the
number of chromosomes by half and the second produces four gametes
each containing the haploid number of chromosomes. Exactly the same
terms are used for the names of the stages, but since meiosis involves two
divisions, the phases are numbered I and II.

The first division is very similar to mitosis and the second division is
exactly the same as mitosis.

BZ^dh^h > BZ^dh^h >>
& Egde]VhZ > * Egde]VhZ >>

cjXaZVg ZckZadeZ cjXaZVg ZckZadeZ
WgZV`h je Vh ^c b^idh^h VcY cjXaZdajh Y^heZghZ
XZcig^daZh gZea^XViZ
Xgdhh^c\ dkZg d[ VcY bdkZ id deedh^iZ
X]gdbVi^Yh bVn dXXjg edaZh d[ i]Z XZaa

]dbdad\djh X]gdbdhdbZh + BZiVe]VhZ >>
eV^g je id [dgb V W^kVaZci
X]gdbdhdbZh
7^kVaZci h]dl^c\ Xgdhh^c\ dkZg i]Vi bVn dXXjg/ a^cZ je hZeVgViZan
VXgdhh ZfjVidg d[
X]gdbVi^Yh bVn XZcigdbZgZ he^cYaZ

WgZV` VcY bVn X]^VhbV Ä ed^ci l]ZgZ Xgdhh^c\
gZXdccZXi id dkZg dXXjgh eajgVa! X]^VhbViV
Vcdi]Zg
X]gdbVi^Y dcZ dg bdgZ X]^VhbViV bVn
[dgb! Vcnl]ZgZ Vadc\ aZc\i]

6i i]Z ZcY d[ egde]VhZ &! V he^cYaZ ^h [dgbZY#

' BZiVe]VhZ > h]dl^c\ Xgdhh^c\
dkZg d[ adc\ X]gdbVi^Yh

W^kVaZcih a^cZ je
VXgdhh ZfjVidg d[
he^cYaZ! ViiVX]ZY
Wn XZcigdbZgZh

he^cYaZ [dgbZY , 6cVe]VhZ >>
Vh ^c b^idh^h
XZcigdbZgZh Y^k^YZ
( 6cVe]VhZ > VcY he^cYaZ
b^XgdijWjaZh ejaa
8ZcigdbZgZh Yd cdi i]Z X]gdbVi^Yh id
Y^k^YZ! jca^`Z b^idh^h# deedh^iZ edaZh

L]daZ X]gdbdhdbZh bdkZ - IZade]VhZ >>
idlVgYh deedh^iZ ZcYh d[
he^cYaZ! XZcigdbZgZh [^ghi!
ejaaZY Wn b^XgdijWjaZh#

) IZade]VhZ >

cjXaZVg ZckZadeZ Vh b^idh^h
gZ"[dgb^c\
cjXaZdajh
gZ"[dgb^c\

Xnid`^cZh^h

gZbV^ch d[ he^cYaZ

X]gdbdhdbZh ]VkZ iZade]VhZ >> Vh b^idh^h iZade]VhZ Wji
gZVX]ZY edaZh d[ he^cYaZ [djg ]Vead^Y YVj\]iZg XZaah [dgbZY

;^\jgZ )#* I]Z hiV\Zh d[ bZ^dh^h ^c Vc Vc^bVa XZaa# CdiZ i]Vi i]Z XZaah VgZ h]dlc l^i] _jhi ild ]dbdad\djh eV^gh d[ X]gdbdhdbZh id
bV`Z ^i ZVh^Zg id jcYZghiVcY i]Z egdXZhh#

,'

Egde]VhZ > In each homologous pair, one
The chromosomes, which have replicated during interphase, now chromosome is a maternal
supercoil. Each one consists of two sister chromatids joined by the chromosome and the other a
centromere.The homologous pairs of chromosomes line up side by side. paternal chromosome.After
crossing over, the chromatids
Although the genes carried by each chromosome pair are identical, recombine to produce new and
the alleles may not be. Exchange of genetic material between the pair can unique combinations of alleles.
occur at this point. Sister chromatids may become entangled, break and This is called recombination.
rejoin so that alleles are exchanged between them during a process called
crossing over. New combinations of alleles are formed and genetic ) <:C:I>8H & ,(
variety in the resulting gametes increases.

The final step in prophase I is the formation of spindle microtubules
and the breakdown of the nuclear envelope.

BZiVe]VhZ >
Chromosomes line up on the equator at the centre of the cell. Each one
attaches by a centromere to the spindle microtubules.The alignment of
the chromosomes is random so that maternal and paternal chromosomes
can appear on either side of one another on the equator.This also
increases the genetic variety in the gametes.

6cVe]VhZ >
The microtubules now contract towards opposite poles.The pairs of sister
chromatids remain together but the homologous pairs are separated.This
is the reduction division where the chromosome number is halved from
diploid to haploid.

IZade]VhZ >
Now spindles break down and a new nuclear envelope forms. Cytokinesis
follows and the cell splits into two cells, each containing only one
chromosome of each homologous pair. Each chromosome, however, still
consists of two sister chromatids at this point.

The second division of meiosis now follows to separate the two sister
chromatids.

Egde]VhZ >>
In each of the two cells resulting from meiosis I, new spindle microtubules
start to form, the chromosomes recoil and the nuclear envelope begins to
break down.

BZiVe]VhZ >>
The nuclear envelope is broken down and individual chromosomes line
up on the equator of each cell. Spindle fibres from opposite ends of the
cell attach to each chromatid at the centromere.

6cVe]VhZ >>
Sister chromatids are separated as the centromere splits and spindle fibres
pull the chromatids to opposite ends of the cell.

IZade]VhZ >>
Nuclear envelopes form around the four new haploid nuclei and the
chromosomes now uncoil.A second cytokinesis occurs, resulting in four
cells.

8dbeVg^c\ b^idh^h VcY bZ^dh^h

Table 4.2 summarises the differences between cell division by mitosis and
by meiosis.

B^idh^h BZ^dh^h

dXXjgh id gZeaVXZ VcY gZeV^g XZaah dXXjgh ^c \VbZiZ [dgbVi^dc

X]gdbdhdbZh a^cZ je ^cY^k^YjVaan dc X]gdbdhdbZh a^cZ je ^c ]dbdad\djh
i]Z he^cYaZ b^XgdijWjaZh eV^gh dc i]Z he^cYaZ b^XgdijWjaZh Vi
bZiVe]VhZ >

egdYjXZh ild XZaah l^i] i]Z hVbZ egdYjXZh [djg ]Vead^Y XZaah
cjbWZg d[ X]gdbdhdbZh Vh i]Z
dg^\^cVa XZaa! i]Z Y^ead^Y cjbWZg

i]Z ild YVj\]iZg XZaah VgZ \ZcZi^XVaan i]Z [djg YVj\]iZg XZaah VgZ jhjVaan

^YZci^XVa \ZcZi^XVaan Y^[[ZgZci

IVWaZ )#' HdbZ Y^[[ZgZcXZh WZilZZc b^idh^h VcY bZ^dh^h#

, >c l]^X] e]VhZ dg e]VhZh d[ bZ^dh^h Yd i]Z [daadl^c\ ZkZcih dXXjg4
V ]dbdad\djh X]gdbdhdbZh hZeVgViZ
W i]Z cjXaZVg ZckZadeZ WgZV`h Ydlc
X i]Z XZcigdbZgZ hea^ih
Y i]Z h^hiZg X]gdbVi^Yh a^cZ je dc i]Z ZfjVidg
Z i]Z X]gdbdhdbZh jcXd^a
[ gZYjXi^dc Y^k^h^dc dXXjgh

Cdc"Y^h_jcXi^dc

Non-disjunction is a failure of homologous pairs of chromosomes to
separate properly during meiosis. It results in gametes that contain either
one too few or one too many chromosomes.Those with too few seldom
survive, but in some cases a gamete with an extra chromosome does
survive and after fertilisation produces a zygote with three chromosomes
of one type, as shown in Figure 4.6.This is called a trisomy.

Trisomy in chromosome 21 results in the human condition known
as Down’s syndrome (Figure 4.7).A gamete, usually the female one,
receives 24 chromosomes instead of 23 and a baby with 47 instead of the
usual 46 chromosomes in each cell is born.

@Vgndine^c\

Chromosomes have unique banding patterns that are revealed if they
are stained with specific dyes during prophase. Each chromosome is a
characteristic length and has its centromere at a fixed place, and each
one has a homologous partner. In a karyogram, chromosomes are
stained and photographed.The image is then manipulated to arrange the
chromosomes in order of their size, as shown in Figure 4.8. Karyograms
indicate the sex of an individual because they show the sex chromosomes,

,)

VWcdgbVa XZaa l^i] cd Xden
d[ i]^h X]gdbdhdbZ

bZ^dh^h

VWcdgbVa XZaa l^i] ild
Xde^Zh d[ i]^h X]gdbdhdbZ

on\diZ ]Vh i]gZZ Xde^Zh d[ [Zgi^a^hVi^dc VWcdgbVa
i]^h X]dbdhdbZ Z\\ XZaa

cdgbVa
heZgb XZaa

;^\jgZ )#+ Cdc"Y^h_jcXi^dc Vi VcVe]VhZ >> d[ bZ^dh^h# Cdc"Y^h_jcXi^dc XVc Vahd dXXjg Vi VcVe]VhZ >#

and they are also used in prenatal diagnosis to check for chromosome
abnormalities.

In the procedure called karyotyping, cells from an unborn child are
collected in one of two ways – chorionic villus sampling (CVS) or
amniocentesis (page 76).The cells are grown in the laboratory and a
karyogram is prepared.This is checked for extra or missing chromosomes.
The procedure is normally used when there is concern about potential
chromosome abnormalities – for example, if the mother is over the age
of 35 years. Down’s syndrome, which is more common in babies of older
mothers, can be detected using this method.

;^\jgZ )#, EZdeaZ l^i] 9dlcÉh hncYgdbZ
]VkZ X]VgVXiZg^hi^X e]nh^XVa [ZVijgZh#

;^\jgZ )#- @Vgnd\gVbh [dg V eZghdc l^i] V cdgbVa X]gdbdhdbZ XdbeaZbZci! VcY [dg V eZghdc l^i] ig^hdbn '& 9dlcÉh hncYgdbZ #
) <:C:I>8H & ,*

EgZcViVa hXgZZc^c\ FjZhi^dch id Xdch^YZg

Obtaining fetal cells for karyotyping by & Karyotyping is a procedure involving medical and
amniocentesis involves taking a sample of amniotic ethical decisions.Who should make the decision
fluid from the mother between weeks 14 and 16 to carry out the procedure – the parents or health
of her pregnancy. Chorionic villus sampling (CVS) care officials? How important are legal and religious
involves taking a sample of cells from the chorionic arguments?
villi, which are the fine projections of the placenta
embedded in the lining of the uterus.This can ' Both procedures carry the risk of a miscarriage.
be done 8–10 weeks into the pregnancy. Both How can this potential risk to the unborn child be
methods carry a small risk of damaging the fetus balanced with the parents’ desire for information?
or even causing a miscarriage. Once the results of What safeguards should be in place when the
the test are known, the parents may be offered the karyotyping procedure is used?
option to terminate the pregnancy if abnormalities
are discovered.The test may reveal an abnormality ( Does the information that can be obtained from the
but it cannot give any indication about the likely karyogram outweigh the risk to the unborn child?
severity of the condition.
) If the karyogram indicates a genetic abnormality,
Vbc^dXZciZh^h should the parents be permitted to consider a
Vi &)Ä&+ lZZ`h d[ egZ\cVcXn termination of the pregnancy?

jiZgjh X]dg^dc^X k^aajh hVbea^c\
Vi -Ä&% lZZ`h d[ egZ\cVcXn

eaVXZciV jiZgjh

cZZYaZ X]dg^dc^X XVi]ZiZg
k^aa^ kV\^cV
[ZiVa XZaah ^c
Vbc^di^X [aj^Y

- 9ZÒ cZ i]Z iZgb È]dbdad\djh X]gdbdhdbZhÉ#
. BZ^dh^h ^h V gZYjXi^dc Y^k^h^dc# L]Vi YdZh i]^h bZVc4
&% =dl bVcn XZaah VgZ [dgbZY l]Zc bZ^dh^h ^c dcZ eVgZci XZaa ^h

XdbeaZiZY4
&& L]Vi ^h V ig^hdbn4
&' HiViZ dcZ ZmVbeaZ d[ cdc"Y^h_jcXi^dc ^c ]jbVch#
&( HiViZ ild X]VgVXiZg^hi^Xh d[ X]gdbdhdbZh i]Vi VgZ jhZY id ^YZci^[n i]Zb

l]Zc `Vgndine^c\#
&) I]Z hdnWZVc ]Vh )% X]gdbdhdbZh ^c ^ih gddi XZaah# L]Vi ^h i]Z cVbZ

\^kZc id i]^h cjbWZg d[ X]gdbdhdbZh4

,+

)#( I]ZdgZi^XVa \ZcZi^Xh

6hhZhhbZci hiViZbZcih

r Define ‘genotype’,‘phenotype’,‘dominant allele’,‘recessive allele’,‘codominant alleles’,‘locus’,‘homozygous’,

‘heterozygous’,‘carrier’ and ‘test cross’.

r Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid.
r State that some genes have more than two alleles (multiple alleles).
r Describe ABO blood groups as an example of codominance and multiple alleles.
r Explain how the sex chromosomes control gender by referring to the inheritance of X andY chromosomes in humans.
r State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.
r Define ‘sex linkage’.
r Describe the inheritance of colour blindness and hemophilia as examples of sex linkage.
r State that a human female can be homozygous or heterozygous with respect to sex-linked genes.
r Explain that female carriers are heterozygous for X-linked recessive alleles.
r Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns

of inheritance.

r Deduce the genotypes and phenotypes of individuals in pedigree charts.

In the study of genetics, there are a number of specialist terms used. It will be helpful to understand and
remember these key words.
Genotype the alleles possessed by an organism; each allele is represented by a letter; chromosomes come in pairs
and so alleles come in pairs – a genotype is therefore represented by a pair of letters – for example, TT or Tt
Phenotype the characteristics of an organism; a characteristic may be an external feature, such as the colour
of flower petals, or internal, such as sickle-cell anemia
Dominant allele an allele that has the same effect on the phenotype when in either the homozygous or
heterozygous state; the dominant allele is always given a capital letter – for example, T
Recessive allele an allele that only has an effect on the phenotype when in the homozygous state; a recessive
allele is always given the lower case of the same letter given to the dominant allele – for example, t
Codominant alleles pairs of alleles that both affect the phenotype when present in the heterozygous state;
these alleles are represented in a different way in genetics; a capital letter is chosen to represent the gene and
then other (superscript) letters represent the alleles (for example, in human blood grouping,A and B are
codominant alleles and are represented as IA and IB)
Locus the specific position of a gene on a homologous chromosome; a gene locus is fixed for a species – for
example, the insulin gene is always found at the same position on chromosome 11 in humans.
Homozygous having two identical alleles at a gene locus; the alleles may both be dominant or both recessive
– for example, TT or tt
Heterozygous having two different alleles at a gene locus – for example, Tt
Test cross testing a dominant phenotype to determine if it is heterozygous or homozygous – for example,
crossing either TT or Tt with tt; if there are any offspring with the recessive phenotype, then the parent with
the dominant phenotype must be heterozygous (Tt)
Carrier an individual with one copy of a recessive allele which causes a genetic disease in individuals that are
homozygous for this allele

) <:C:I>8H & ,,

Parental generation the original 9ZiZgb^c^c\ \ZcdineZh VcY e]ZcdineZh ^c
\ZcZi^Xh egdWaZbh
parent individuals in a series of
Jh^c\ V EjccZii \g^Y
experimental crosses
A genetic diagram called a Punnett grid can be used to work out all the
F1 generation the offspring of the possible combinations of alleles that can be present in the offspring of two
parental generation parents whose genotypes are known. Punnett grids show the combinations
and also help to deduce the probabilities of each one occurring.
F2 generation the offspring of a
cross between F1 individuals When working out a problem, it is helpful to follow a few simple steps.

r Choose a letter to represent the gene. Choose one that has a distinctly

different upper and lower case for the alleles – so for example O, P and
W would not be good choices. It is useful to base the letter on the
dominant phenotype – so for example R = red could be used for
petal colour.

r Represent the genotype of each parent with a pair of letters. Use a single

letter surrounded by a circle to represent the genotype of each gamete.

r Combine pairs of the letters representing the gametes to give all the

possible genotypes of the offspring.A Punnett grid provides a clear way
of doing this.

r From the possible genotypes, work out the possible phenotypes of the

offspring.
Worked examples 1 and 2 show how to tackle genetics problems using
these steps.

Ldg`ZY ZmVbeaZ &

Suppose that fur colour in mice is determined by a single gene. Brown fur is dominant to white.A mouse
homozygous for brown fur was crossed with a white mouse. Determine the possible genotypes and phenotypes
of the offspring.

Step 1 Choose a letter. Brown is dominant so let eVgZciVa e]ZcdineZh/ Wgdlc l]^iZ
B = brown fur and b = white fur. eVgZciVa \ZcdineZh/ WW
\VbZiZh/ 77 W W
Step 2 We are told the brown mouse is EjccZii \g^Y [dg ;&/ 7 7
homozygous so its genotype must be BB.
Since white is recessive, the genotype of \VbZiZh [gdb
the white mouse can only be bb. If a B Wgdlc eVgZci
were present, the mouse would have brown
fur. 77

Step 3 Set out the diagram as on the right. \VbZiZh [gdb W 7W 7W
Step 4 The Punnett grid shows that all the l]^iZ eVgZci Wgdlc Wgdlc

offspring will be phenotypically brown and 7W 7W
their genotype will be Bb. Wgdlc Wgdlc

W

,-

Ldg`ZY ZmVbeaZ '

Seed shape in the pea plant is controlled by a single gene. Smooth shape is dominant to wrinkled shape.A plant
that was heterozygous for smooth seeds was crossed with a plant that had wrinkled seeds. Determine the
possible genotypes of the offspring and the phenotype ratio.

Step 1 Choose a letter. Smooth is the dominant trait eVgZciVa e]ZcdineZh/ hbddi] lg^c`aZY
but S and s are hard to distinguish so use eVgZciVa \ZcdineZh/
another letter, such as T. \VbZiZh/ Ii ii i
EjccZii \g^Y [dg ;&/ I i i
Step 2 We are told the smooth plant is heterozygous
so its genotype must be Tt. \VbZiZh [gdb
Since ‘wrinkled’ is a recessive trait, the genotype hbddi]"hZZY eVgZci
of the wrinkled seed plant must be tt.
Ii
Step 3 Set out the diagram as shown opposite,
in exactly the same way as before. Notice \VbZiZh [gdb i Ii ii
that, in this case, the smooth-seeded parent lg^c`aZY"hZZY eVgZci hbddi] lg^c`aZY
produces two different types of gamete
because it is heterozygous. i Ii ii
hbddi] lg^c`aZY
Step 4 Here the Punnett grid shows us that half of
the offspring will have smooth seeds with
the genotype Tt and half will have wrinkled
seeds with the genotype tt.
The ratio of the phenotypes is 1 :1.

&* 9ZÒ cZ ZVX] d[ i]Z [daadl^c\ iZgbh#

V \ZcdineZ Y gZXZhh^kZ VaaZaZ \ ]ZiZgdon\djh
] XVgg^Zg
W e]ZcdineZ Z adXjh ^ iZhi Xgdhh

X Ydb^cVci VaaZaZ [ ]dbdon\djh

&+ >[ gZY G ^h Ydb^cVci id nZaadl g! l]Vi ^h i]Z e]ZcdineZ d[ ZVX] d[ i]Z

[daadl^c\ \ZcdineZh4

V GG W Gg X gg

&, L]Vi ldjaY WZ i]Z \VbZiZh egdYjXZY Wn V eVgZci l^i] ZVX] d[ i]Z

[daadl^c\ \ZcdineZh4

V GG W gg X Gg

&- 8den VcY XdbeaZiZ i]Z EjccZii \g^Y \VbZiZh [gdb
deedh^iZ# <gZZc hZZY Xdadjg < ^h \gZZc eVgZci
Ydb^cVci id ejgeaZ hZZY Xdadjg \#
<\

\VbZiZh [gdb < <<
\gZZc eVgZci \gZZc

\

) <:C:I>8H & ,.

<ZcdineZ E]ZcdineZ dg WaddY \gdje 8dYdb^cVcXZ VcY bjai^eaZ VaaZaZh

>6>6 6 In the two worked examples above, one of the alleles completely
>6^ 6 dominates the other, so in a heterozygous genotype the phenotype is
>7>7 7 determined solely by the dominant allele. In codominance, both alleles
>7^ 7 have an affect on the phenotype.
>6>7 67
^^ D The examples of the mouse coat colour and the smooth and wrinkled
peas are both known as monohybrid crosses because they involve
IVWaZ )#( =jbVc WaddY \gdjeh VcY i]Z^g just one gene with two alleles: brown B and white b, or smooth T and
\ZcdineZh# wrinkled t.There are many other cases in which genes have more than
two alleles. One example of this is human blood groups.

The ABO human blood grouping is an example of both codominance
and multiple alleles.There are three alleles – IA, IB and i. IA and IB are
codominant and both are dominant to i.This results in four different
phenotypes or blood groups.

A person’s blood group depends on which combination of alleles he
or she receives. Each person has only two of the three alleles and they
are inherited just as though they are alternative alleles of a pair.Table 4.3
shows the possible combinations of alleles and the resulting phenotypes.

Ldg`ZY ZmVbeaZ (\VbZiZh [gdb
Celia is blood group A and her husband Sanjeev is blood group B.Their daughter Sally is blood group O.8Za^V
Determine the genotypes of Celia and Sanjeev.
Step 1 The alleles are represented by IA, IB and i.
Step 2 To be blood group A, Celia could have genotype IAIA or IAi.

To be blood group B, Sanjeev could have genotype IBIB or IBi.
To be blood group O, Sally could only have the genotype ii.
Step 3 Each of Sally’s two alleles have come from her parents, so she must have received one i from her mother
and one i from her father, as shown in the Punnett grid.

\VbZiZh [gdb
HVc_ZZk

>7 ^

>6

^^
^ HVaan

\gdje D

Step 4 Celia is blood group A so must have the genotype IAi and Sanjeev’s genotype has to be IBi.

-%

Ldg`ZY ZmVbeaZ )

Hair shape in humans is a codominant characteristic. Straight hair and curly hair are codominant alleles and the
heterozygote has wavy hair. Daryll and Shaniqua both have wavy hair. Deduce the probabilities that their children
will have straight hair, curly hair or wavy hair.

HS = straight hair and HC = curly hair. eVgZciVa e]ZcdineZh/ lVkn lVkn

Since both Daryll and Shaniqua have wavy hair their eVgZciVa \ZcdineZh/ =H=8 =H=8
genotypes must be HSHC. \VbZiZh/ =H =8 =H =8
EjccZii \g^Y/
The Punnett grid shows that the probabilities of \VbZiZh [gdb
a child inheriting each hair type are: H]Vc^fjV
r TUSBJHIU IBJS
r DVSMZ IBJS =H =8
r XBWZ IBJS
=H=H =H=8
\VbZiZh [gdb =H higV^\]i lVkn
9Vgnaa
]V^g ]V^g

=H=8 =8=8
=8 lVkn Xjgan

]V^g ]V^g

HZm X]gdbdhdbZh VcY i]Z Xdcigda d[ \ZcYZg

Humans have one pair of chromosomes that determine whether
the person is male or female.These chromosomes are called the sex
chromosomes. Each person has one pair of sex chromosomes, either
XX or XY, along with 22 other pairs known as autosomes.The X
chromosome is longer than the Y and carries more genes. Human females
have two X chromosomes and males have one X and one Y.

Sex chromosomes are inherited in the same way as other chromosomes.

eVgZciVa e]ZcdineZh/ [ZbVaZ bVaZ
eVgZciVa \ZcdineZh/ MN
\VbZiZh/ MM M N
EjccZii \g^Y [dg ;&/ M M

\VbZiZh [gdb
bVaZ eVgZci

MN

\VbZiZh [gdb M MM MN
[ZbVaZ eVgZci [ZbVaZ bVaZ

M MM MN
[ZbVaZ bVaZ

) <:C:I>8H & -&

MN The ratio of phenotypes female : male is 1 :1.This means, at fertilisation,
there is always a 50% chance that a child will be a boy and 50% that it will
]dbdad\djh iZhi^h be a girl.
gZ\^dc YZiZgb^c^c\
[VXidg HZm X]gdbdhdbZh VcY \ZcZh

[VXidg K>>> The sex chromosomes not only carry the genes that control gender, the X
^bedgiVci ^c chromosome also carries genes called sex linked or X-linked genes.These
WaddY Xadii^c\ genes occur only on the X chromosome and not on the Y chromosome,
;^\jgZ )#. M VcY N X]gdbdhdbZh# which is much shorter (Figure 4.9).The Y chromosome carries alleles that
are mainly concerned with male structures and functions.
Sex linkage the pattern of
inheritance that is characteristic Sex linkage has a significant effect on genotypes. Females have two
for genes located on the X X chromosomes, so they have two alleles for each gene and may be
chromosome homozygous or heterozygous. In a female, a single recessive allele will be
masked by a dominant allele on her other X chromosome. Males only
have one allele on their X chromosome with no corresponding allele on
the Y chromosome, so a recessive allele will always be expressed in a male.

A female who is heterozygous for a sex-linked recessive characteristic
that does not affect her phenotype is called a carrier.

:mVbeaZh d[ hZm"a^c`ZY X]VgVXiZg^hi^Xh

Two examples of sex-linked human characteristics are hemophilia and
red–green colour blindness.

Hemophilia is a condition in which the blood of an affected person
does not clot normally. It is a sex-linked condition because the genes
controlling the production of the blood-clotting protein factor VIII
are on the X chromosome.A female who is XHXh will be a carrier
for hemophilia.A male who has the recessive allele XhY will be a
hemophiliac. Figure 4.10 is a pedigree chart showing how a sex-linked
condition like hemophilia may be inherited. Notice that hemophilia
seldom occurs in females, who would have to be homozygous for the
recessive allele XhXh.This condition is usually fatal in utero, resulting in a

]Zbde]^a^VX bVaZ cdgbVa bVaZ cdgbVa [ZbVaZ cdgbVa [ZbVaZ XVgg^Zg

;^\jgZ )#&% EZY^\gZZ [dg V hZm"a^c`ZY gZXZhh^kZ Y^hZVhZ! hjX] Vh ]Zbde]^a^V#

-'

miscarriage.Today, hemophilia is treated by giving the affected person the
clotting factor they cannot produce.

A person with red–green colour blindness has difficulty distinguishing
between red and green. Red–green colour blindness is inherited in a similar
way to hemophilia.A female who is XBXb is a carrier for colour blindness
and a male with just one copy of the recessive allele will be colour blind.
Remember that a man cannot be a carrier for a sex-linked gene.

Ldg`ZY ZmVbeaZ *

A woman who is homozygous for normal vision married a man who is red–green colour blind.
Determine the possible types of vision inherited by their two children, one girl and one boy.

Step 1 Standard letters are used for these alleles – normal vision is XB and colour blind is Xb.The X is
always included.

Step 2 The woman is homozygous for normal vision so her genotype must be XBXB.
Since the man is colour blind, his genotype must be XbY.

Step 3 Set out the diagram as below.

eVgZciVa e]ZcdineZh/ ldbVc bVc
eVgZciVa \ZcdineZh/ MWN
\VbZiZh/ M7M7 MW N
EjccZii \g^Y [dg ;&/ M7 M7

\VbZiZh [gdb bVc

MW N

\VbZiZh [gdb ldbVc M7MW M7N
M7 \^ga! cdgbVa Wdn! cdgbVa

k^h^dc! XVgg^Zg k^h^dc

M7MW M7N
M7 \^ga! cdgbVa Wdn! cdgbVa

k^h^dc! XVgg^Zg k^h^dc

Step 4 The Punnett grid shows that a daughter will have normal vision, but be a carrier for red–green colour
blindness.A son will have normal vision.

EZY^\gZZ X]Vgih

Pedigree charts, like the one shown in Figures 4.10 and 4.11 (overleaf),
are a way of tracing the pattern of inheritance of a genetic condition
through a family. Specific symbols are always used, and the chart is set out
in a standard way.The horizontal lines linking the male and female in a
generation indicate a marriage (or mating) and the vertical lines indicate
their offspring. Offspring are shown in the order of their birth. For
example, in the family shown in Figure 4.11, the oldest individual affected
with the genetic condition is II2, who is a male.

) <:C:I>8H & -(

i]ZhZ cjbWZgh I
gZegZhZci i]Z
\ZcZgVi^dc i]ZhZ cjbWZgh gZegZhZci i]Z
^cY^k^YjVah ^c V \ZcZgVi^dc
& '

II

&' () *+

III

@Zn &' () * +, -
jcV[[ZXiZY jcV[[ZXiZY ]ZiZgdon\diZ ]ZiZgdon\diZ
[ZbVaZ bVaZ V[[ZXiZY V[[ZXiZY XVgg^Zg XVgg^Zg
[ZbVaZ bVaZ [ZbVaZ bVaZ

;^\jgZ )#&& I]^h eZY^\gZZ X]Vgi h]dlh i]Z dXXjggZcXZ d[ V \ZcZi^X XdcY^i^dc `cdlc Vh WgVX]nYVXinan h]dgi Ò c\Zgh ^c V [Vb^an#

Ldg`ZY ZmVbeaZ +

Cystic fibrosis (CF) is a genetic disorder that causes the excessive production
of thick sticky mucus. It is due to a recessive allele that is not sex linked.The I

pedigree chart below shows two generations of a family.A filled-in symbol & '

represents an individual who has cystic fibrosis.

Deduce the genotypes of the parents I1 and I2.

Deduce the probability that II1 is heterozygous. II

&'

Step 1 Cystic fibrosis is a recessive disorder so the ‘normal’ condition, without cystic fibrosis, is dominant.
It is useful to choose N to represent the normal allele.

Step 2 Neither of the parents, I1 and I2, have cystic fibrosis so both must have at least one normal allele N.
Since cystic fibrosis is recessive and II2 has the condition, she must have the genotype nn.
II2 received one allele from each of her parents so both of them must have passed one n allele to
her. Both parents must have one n but they do not have cystic fibrosis so their genotype must be
heterozygous Nn.
The pedigree chart could now be redrawn, to show that the parents are heterozygous carriers.

I '

&

II '

&

-)

Step 3 Now that both parents are known to be heterozygous, a Punnett grid can be drawn.

\VbZiZh [gdb I&
Cc

\VbZiZh [gdb I' C CC Cc
cdgbVa cdgbVa

c Cc cc
cdgbVa II' l^i] 8;

Step 4 Person II1 does not have cystic fibrosis and so could have the allele combination shown by any of the
shaded boxes.The probability of being heterozygous is 2 out of 3, or 32, or 66%.

Ldg`ZY ZmVbeaZ ,

The pedigree chart below shows the family history of a recessive human condition called woolly hair.A filled-in
symbol indicates that the person has woolly hair. Deduce whether this condition is sex linked or not.

I '

&

II

& '(

III

& '(

Step 1 Remember that in a sex-linked condition, the allele occurs only on the X chromosome and males only
have one X chromosome.

Step 2 Using N to represent the condition, we can see that female III1 must be nn as she has the condition and
thus has inherited one n from each parent.

Step 3 If woolly hair is not sex linked, both her parents would be Nn as they have normal hair.
Step 4 If it is sex linked, her mother (II2) would be XNXn and her father (II3) would be XnY.This would

mean he has the recessive allele and no dominant allele. If the condition is sex linked, he would have
woolly hair, which he does not.This proves that it is not sex linked.

) <:C:I>8H & -*

Ldg`ZY ZmVbeaZ -
The pedigree chart below shows the inheritance of a particular genetic condition in a family.A filled in circle or
square means that the individual is affected, that is, shows the genetic condition.The condition is not sex linked.
Deduce whether the characteristic is dominant or recessive.

I

&'

II '( )* +

&

III

&'( ) *+

We can see that the genetic condition is dominant because of the following reasons:

r affected individuals occur in every generation
r every affected individual has at least one affected parent
r two affected parents (II3 and II4) can have a non-affected child (III4), so the parents must be heterozygous.

<ZcZi^Xh e^dcZZgh gZ_ZXiZY VcY ^\cdgZY

Gregor Mendel (1822–1884) was an contained the entire basis of modern genetics.
Augustinian monk in the Abbey of St Thomas in
Brno, a town in what is now the Czech Republic. In 1951, two years before the structure of DNA
Over a period of seven years, he cultivated and was determined, Dr Barbara McClintock presented
tested different pea plants and studied their visible a paper on ‘jumping genes’ at a symposium at
characteristics. In 1866, he published a paper on the the Cold Spring Harbor research laboratories in
inheritance of characteristics in pea plants, which he North America. She explained how genes could be
called ‘Experiments on Plant Hybridization’, in The transferred from one chromosome to another. Her
Proceedings of the Natural History Society of Brünn. In work was rejected by fellow scientists and ignored for
it, he set out his two laws of inheritance.Although 30 years until rediscovered. Now she is recognised as
Mendel sent copies to well-known biologists, his ideas a pioneer in the field and her work is acknowledged
were rejected. For the next 35 years, his paper was as a cornerstone of modern genetics. In 1983, Dr
effectively ignored yet, as scientists later discovered, it McClintock received a Nobel Prize for her work.

FjZhi^dch id Xdch^YZg

<gZ\dg BZcYZa! \ZcZi^Xh e^dcZZg# & Why is the work of some scientists ignored while that of others
becomes readily accepted?

' How important is it for a new theory to be presented in a famous
journal or at a well-attended meeting?

( Do you think Mendel’s work was ignored because it was not widely
published, or because he was not a well-known scientist, or for some
other reason?

) Barbara McClintock was a young woman when she presented her
work. Her work represented a completely different view of how
genes might behave. How significant is this type of paradigm shift in
gaining acceptance for a new theory or discovery?

-+

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h]dlh V eVgi^XjaVg \ZcZi^X XdcY^i^dc4

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)#) <ZcZi^X Zc\^cZZg^c\ VcY
W^diZX]cdad\n

6hhZhhbZci hiViZbZcih

r Outline the use of the polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.
r State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size.
r State that gel electrophoresis of DNA is used in DNA profiling.
r Describe the application of DNA profiling to determine paternity and also in forensic investigations.
r Analyse DNA profiles to draw conclusions about paternity or forensic investigations.
r Outline three outcomes of the sequencing of the complete human genome.
r State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them

is unchanged because the genetic code is universal.

r Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell),

restriction enzymes (endonucleases) and DNA ligase.

r State two examples of the current uses of genetically modified crops or animals.
r Discuss the potential benefits and possible harmful effects of one example of genetic modification.
r Define ‘clone’.
r Outline a technique for cloning using differentiated animal cells.
r Discuss the ethical issues of therapeutic cloning in humans.

Genetic engineering and biotechnology have opened up new
opportunities in forensic science, agriculture, medicine and food
technology.As knowledge has grown, science has enabled people to
manipulate the unique genetic identity of organisms. Gene transfer,
cloning and stem cell research have raised questions about the safety and
ethics of techniques that have been unknown to previous generations.

) <:C:I>8H & -,

9C6 egdÒ a^c\

At a crime scene, forensic scientists check for fingerprints because a
person’s fingerprint is unique and can be used to identify them. Forensic
scientists also collect samples of hair, skin, blood and other body fluids left
at a crime scene because they all contain a person’s DNA and that too is a
unique record of their presence.

Matching the DNA from a sample to a known individual is called
DNA profiling. In forensic science, DNA profiles from crime scenes can
be used to establish the possibility of guilt or prove a suspect innocent
(Figure 4.13). DNA profiling can also be used to determine paternity.
For example, a woman might claim that a particular man is the father of
her child. By comparing DNA samples from all three individuals – the
woman, the man and the child – paternity can be established.

I]Z edanbZgVhZ X]V^c gZVXi^dc E8G

DNA profiles can only be done if there is sufficient DNA to complete the
procedure. Sometimes, at a crime scene or when a body is found after a
very long time, only a minute amount can be collected.The polymerase
chain reaction is a simple method that makes millions of copies of tiny
amounts of DNA so there is sufficient to produce a profile.This is done
at high temperature using a special type of DNA polymerase enzyme.
Technicians must take great care when handling the original sample so
that it is not contaminated with their own or other DNA.

FjZhi^dch id Xdch^YZg 9C6 egdÒ aZ YViVWVhZh

& DNA profiles do not show In the USA, the FBI has a national database of DNA profiles
individual base sequences but from convicted criminals, suspects, missing persons and crime scenes.
only identify repeated sequences. The data that is held may be used in current investigations and to solve
How much confidence should be unsolved crimes.There are many commercial laboratories that carry
placed on DNA evidence? out DNA profiling analysis on behalf of law enforcement agencies.
Many of them check 13 key ‘short tandem repeat’ sequences in DNA
' How secure is DNA profiling? samples, which vary considerably between individuals.The FBI has
( What are the implications for recommended that these should be used because they provide odds of
one in a thousand million that two people will have the same results.
society if the authorities were
to hold a DNA profile for every CODIS is a computer software program that operates the national
person? database of DNA profiles. Every American State has a statutory right
) What safeguards should be in to establish a DNA database that holds DNA profiles from offenders
place to protect the rights of convicted of particular crimes. CODIS software enables laboratories to
individuals whose DNA profiles compare DNA profiles electronically, linking serial crimes to each other
have been placed on a database and identifying suspects from profiles of convicted offenders. CODIS
but who have not been convicted has contributed to thousands of cases that have been solved by matching
of a crime? crime scene evidence to known convicted offenders.
* Is it right to convict a person on
DNA evidence alone?

--

<Za ZaZXigde]dgZh^h

Gel electrophoresis is a method used to separate fragments of DNA on
the basis of size and the electric charge they carry. It can identify natural
variations found in every individual’s DNA.

Any DNA sample usually contains long molecules that are too large
to be used for profiling. Enzymes, called restriction enzymes, are used
to cut DNA into fragments at very precise points in the base sequences.
Since each individual has a unique DNA sequence, the positions of these
cutting sites will vary, giving a mixture of different fragment sizes.

The DNA fragments are placed in a well in a plate of gel (a jelly-like
material) and an electric field is applied. Each DNA fragment has a small
negative charge and so will move in the electric field, through the gel.
The distance a fragment can move depends on its size – smaller fragments
move most easily through the gel matrix and travel further, while larger
fragments are left behind close to their starting point.After the fragments
have been separated in the gel, they are stained and produce a unique
pattern of bands called a DNA profile (Figures 4.12 and 4.13).

I]Z =jbVc <ZcdbZ Egd_ZXi

In 1990, the Human Genome Project was started as an international
collaboration to determine the entire base sequence of the human
genome.The project was publicly funded in a number of countries and
the sequencing of three billion base pairs was completed in 2003.Work
continues on locating genes and mapping their specific positions on
chromosomes. Identifying and studying the proteins produced by these
genes may soon give a better understanding of genetic disorders. Since
2003, other genome-sequencing projects have been undertaken to gather
data on populations from different parts of the world and analyse genetic

WaddY hiV^c Vi hXZcZ d[ Xg^bZ

&'( )*+,

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9C6 egdÒ aZ# I]Z hVbeaZ d[ 9C6 ^h bVg`ZY l^i] V gVY^dVXi^kZ hjWhiVcXZ! hd i]Z 9C6 [djcY Vi i]Z hXZcZ d[ V Xg^bZ XdbeVgZY l^i]
WVcY^c\ eViiZgc VeeZVgh e^c` jcYZg jaigVk^daZi a^\]i# I]Z eViiZgc ^h egZhZgkZY Wn egdÒ aZh [gdb hZkZc hjheZXih# L]^X] hjheZXi
Veean^c\ gVY^d\gVe]^X Ò ab id i]Z \Za# lVh Vi i]Z hXZcZ d[ i]Z Xg^bZ4 L]Vi ^h i]Z
Zk^YZcXZ id hjeedgi ndjg VchlZg4

) <:C:I>8H & -.

GM sheep benefit humans variation. Simply knowing the base sequence of a chromosome does not
have much scientific value, but knowing the sequence of the genes on that
Factor XI was first recognised chromosome will be of great value in molecular medicine, as well as in
in 1953. Factor XI is part of forensic science and the study of evolution.
the cascade of clotting factors
that form the chain leading to a Some of the medical benefits that are already being investigated include:
protective clot.The incidence of
Factor XI deficiency is estimated r improved diagnosis of disease – faulty genes can be found during
at 1 in 100 000.Although, in some
people, the symptoms are similar to prenatal diagnosis, for example, allowing earlier treatment
hemophilia, it is not a sex-linked
condition and it affects men and r earlier detection of genetic susceptibility to disease so that
women equally. In many countries,
treatment involves obtaining factor environmental factors that trigger the disease can be avoided
XI from fresh-frozen plasma and
since factor XI is not concentrated r better identification of carriers of genetic conditions
in plasma, considerable amounts of r gene therapy, which aims to repair or replace a faulty gene
it are needed. It is hoped that the r drug design to find new classes of drugs that act on specific genes
production of clotting factors in r pharmacogenomics, where the drug is tailored specifically to an
GM sheep’s milk will lead to new
and better treatments. individual.

<ZcZ iZX]cdad\n

Gene technology, which is also called genetic modification (GM)
or genetic engineering, involves the transfer of genes from one species
to another in order to produce new varieties of organisms with useful or
desirable characteristics.

Selective plant and animal breeding has been carried out by humans
for thousands of years as people tried to develop cattle that produced
high milk yields or crops with better resistance to disease, for example.
In these cases, animals or plants of the same species were chosen for
breeding because of their particular characteristics. Over many generations
of selection, the desired characteristics increase in frequency in the
population.

Gene technology gives us the new ability to transfer genes from one
species to another completely different species in just one generation. For
example, bacterial genes have been transferred to plants, human genes
transferred to bacteria and spider genes transferred to a goat.

:i]^Xh VcY i]Z =jbVc FjZhi^dch id Xdch^YZg
<ZcdbZ Egd_ZXi
& Does simply knowing the sequence of the three billion base
Although the sequencing of the bases of pairs of the human chromosomes tell us anything about
the human genome has been completed, what it means to be human?
the task of identifying all of the genes is
ongoing.As these genes are found, it would ' Should third parties such as health insurance companies
be possible for a person to be screened for have the right to see genetic test results or demand that a
particular genes that could affect them – for person is screened before offering insurance cover or setting
example, by increasing their susceptibility the level of premiums?
to cancer or the likelihood that they will
develop Alzheimer’s disease in later life. ( If treatment is unavailable, is it valuable to provide
knowledge of a genetic condition that a person may carry?

) Knowledge of an individual’s genome has implications for
other members of their families. Should their rights be
protected?

.%

Gene transfer is possible because the genetic code is universal. No New developments in genetic
matter what the species, the genetic code spells out the same information modification
and produces an amino acid sequence in one species that is exactly the
same in any other species. While strawberries, pineapples,
sweet peppers and bananas have
Usually, in gene transfer, only single genes are used – for example, the all been genetically modified to
gene for producing human blood-clotting factor XI has been transferred remain fresh for longer, a new
to sheep, which then produce the factor in their milk. variety of golden-coloured rice has
been genetically modified so that it
I]Z iZX]c^fjZ d[ \ZcZ igVch[Zg contains high levels of a substance
called beta-carotene. Beta-carotene
One of the first important uses of gene transfer was to produce insulin gives carrots their orange colour
for diabetic patients who do not produce insulin properly. Many years but, more importantly, the body
ago, insulin was obtained from cow or pig pancreases but the process was converts it to vitamin A, which is
difficult and the insulin was likely to be contaminated.Today, diabetics essential for the development of
inject themselves with human insulin that has been made by modified pigments in the retina of the eye.
E. coli bacteria (Figure 4.14, overleaf). Three genes had to be introduced
There are key three steps in the process: into rice so it could produce beta-
carotene.Two of these came from
r obtaining the desired human insulin gene in the form of a piece of daffodils and the third was taken
from a bacterium.
DNA
Enriched Golden RiceTM is a
r attaching this DNA to a vector, which will carry it into the host cell valuable dietary supplement for
people whose diet is low in vitamin
(E. coli) – the vector used is the plasmid found inside the bacterium A and who might otherwise suffer
vision problems or blindness. Since
r culturing E. coli bacteria so that they translate the DNA and make Golden RiceTM was developed in
the 1990s, research has continued
insulin, which is collected. into its use and help in enriching
diets. Some interesting and
<ZcZi^XVaan bdY^Ò ZY dg\Vc^hbh <BDh controversial issues have arisen
about the ownership of the rights
By 2009, almost 100 plant species had been genetically modified and to the seeds, the flavour of the rice
many trials have taken place to assess their usefulness. In comparison, and the publication of research data
there are very few examples of genetically modified animal species. from experimental studies.You
Most genetic engineering has involved commercial crops such as maize, may like to read more about this
potatoes, tomatoes and cotton. Plants have been modified to make them in Plant Physiology, March 2001,
resistant to pests and disease and tolerant to herbicides. Genetically vol. 125, pages 1157–1161,
engineered animals, on the other hand, have mainly been farmed for the www.plantphysiol.org.
products of the inserted genes – most common are proteins such as
factor XI and B1 antitrypsin, which are needed for the treatment of ) <:C:I>8H & .&
human diseases.

=ZgW^X^YZ idaZgVcXZ
Herbicides are used to kill weeds in crop fields but they are expensive
and can affect local ecosystems as well as cultivated areas. One commonly
sprayed and very powerful herbicide is glyphosate, which is rapidly broken
down by soil bacteria. For maximum crop protection, farmers needed to
spray several times a year. But now, the genes from soil bacteria have been
successfully transferred into maize plants making them resistant to the
herbicide.

Farmers can plant the modified maize seeds, which germinate along
with the competing weeds. Spraying once with glyphosate kills the weeds
and leaves the maize unaffected.The maize then grows and out-competes
any weeds that grow later when the glyphosate has broken down in the
soil.Yields are improved and less herbicide has to be used.

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