Notes_gm

MUTATION

7.1 Mutation classification and types
7.2 Gene Mutation
7.3 Chromosomal Mutation

7.1 Mutation Classification and types

Learning Outcome:

a) Define mutation.

b) Class of mutation:

i. Gene/point mutation
ii. Chromosomal mutation

c) Types of mutation:

i. Spontaneous mutation (occur naturally e.g.: non-disjunction)
ii. Induced mutation (involve human intervention e.g.: exposure to

mutagen)

d) Define mutagen

e) State types of mutagen:

i. Physical (e.g.: UV rays and gamma rays)
ii. Chemical (e.g.: colchicine and ethidium bromide)

Blue lobster is a kind of mutant (an organism carrying a gene
that has undergone a mutation) arising from a mutation.

What is a mutation?

A change in the nucleotide sequence of an organism’s
DNA or in the DNA or RNA of virus. (Campbell, 11th Ed.)

Any change in DNA that may include change in the
nucleotide base pair of a gene or a rearrangement of
genes within the chromosome. (Solomon, 10th ed.)

Any change made in the nucleotide sequence of DNA
and become source of new variation for a species.

(Mader, 12th Ed.)

Mutation is a permanent change in the amount,
arrangement or structure of the DNA of an organism.

Mutation produce new trait that can be inherited.

Mutation can occur in gamete cells or somatic cells.

Mutation that occur in gamete cells are inherited.
Mutation that occur in somatic cells are NOT PASSED
onto offspring but can only be inherited by daughter
cells produced by MITOSIS.

Mutation can occur during
DNA replication

Many mutations result in
the change of a protein
therefore the protein
cannot function as it
should be.

Class of mutation

Gene / Point mutation Chromosomal mutation
- A change in a single nucleotide
- Abnormalities in chromosomal structure
pair of DNA & changes in chromosome number

• Base substitution Chromosomal Chromosomal
• Base insertion
• Base deletion aberration number alteration
• Base inversion
• Translocation • Aneuploidy
• Deletion • Euploidy/
• Inversion
• Duplication polyploidy

Types of mutation

Spontaneous mutation Induced mutation

• Occur in natural condition • Involve human intervention
(random and rare event).
• Occurs when organism
• Mistakes in base exposed to mutagen - a
pairing/arrangement that substance that can cause
happen spontaneously much higher rate of
during DNA replication. mutation

• E.g : error in DNA • Physical mutagen &
replication (lack of DNA chemical mutagen
repair)

A chemical and physical agents that interacts with
DNA and can cause mutation. (Campbell, 11th Ed.)

Chemical or physical agents that increase the chance
of mutations.(Mader, 12th Ed.)

Operate either by causing changes in the DNA of the
genes or by causing chromosome damage.

TWO types of mutagen:
Chemical mutagen
Physical mutagen

Types of mutagen

Physical mutagen Chemical mutagen

• Ultraviolet (UV) ray • Colchicine
• Ionizing agent – gamma • Ethidium bromide
• Mustard gas
ray or X-ray

Colchicum autumnale = meadow saffron

A mutant is an individual or new genetic character
arising or resulting from an instance of mutation.



Learning Outcome:

a) Define gene/ point mutation

b) State the four types of gene mutation:
i. Base substitution
ii. Base insertion
iii. Base deletion
iv. Base inversion

e) State the effect of base substitution (missense,
nonsense and silent mutation) and base insertion and
base deletion(frameshift mutation).

Change in a single nucleotide pair in DNA sequence / of
a gene. (Campbell, 11th Ed.)

Altered genes whose sequence of bases differs from
the original sequence. (Mader, 12th Ed.)

Arise due to spontaneous pairing errors that occur
during DNA replication.

It leads to change in amino acid sequence from the
point of mutation, thus changes the protein.

Also known as point mutation



1. Base substitution
2. Base inversion
3. Base insertion
4. Base deletion

Changes in
base sequence

1) Base substitution

The replacement of one nucleotide and its partner
with another pair of nucleotides. (Campbell, 11th Ed.)

Base substitution
can cause :
1) Silent mutation
2) Missense

mutation
3) Nonsense

mutation

(Campbell, 11th Ed./p.408)

Silent mutation : A change in nucleotide pair may
transform one codon into another that is translated
into same amino acid. (Campbell, 11th Ed.)

No observable effect on the phenotype.

Missense mutation : Codon still code for an amino acid
but change the indicated amino acid. (Campbell, 11th Ed.)

● In the DNA, the mutant (sickle-cell) template strand has
an A while the wild type template has T.

● The mutant mRNA has a U instead of an A in one codon.

● The mutant haemoglobin has a valine (Val) instead of
glutamic acid (Glu).

Nonsense mutation : Change an amino acid codon into

a stop codon. Lead to non-functional protein. (Campbell,

11th Ed.)

2) Base Insertion

The addition of nucleotide pairs in a gene. (Campbell,

11th Ed.)

Base Insertion

AT AT
GC
Normal CG GC
TA
TA CG
AT
GC

TA

T A
A T

3) Base Deletion
The loss of nucleotide pairs in a gene. (Campbell, 11th Ed.)

Normal AT Base Deletion
GC
CG AT
TA GC
TA CG
AT TA
AT

Insertion or deletion of nucleotides may alter the
reading frame of genetic message.

It caused frameshift mutation

Occurs whenever the number of nucleotides
inserted or deleted is not in multiple of three

Many of these deletion/insertion start in the
middle of a codon

Shifting the reading frame by one or two bases

cause the gene to be read in the wrong three base
groups (codon) starting from the point of mutation.

From the mutation point, it abrupt the coding
sequence of amino acid.

Changes in codons results in changes in amino
acids

Causing different polypeptide to be produced

Effect : usually harmful to human

E.g.: Major Thalassemia (mutant homozygote
alleles)

4) Base Inversion

Two nucleotide pairs or more are inverted in the
DNA sequences. (Campbell, 11th Ed.)

Normal AT Base Inversion
GC
CG AT
TA GC
TA TA
AT CG
TA
AT

Gene/point mutation

AT

Normal G C
C G

TA

TA

Base Insertion AT

AT Base Substitution Base Deletion Base Inversion
GC
CG AT AT AT
GC GC GC GC
TA CG CG TA
TA GC TA CG
AT TA AT TA
AT AT