MUTATION WITH MADAM HIDAH

1. TABLE 1 shows the summary of the result of abnormalities that occur during gametogenesis.

Individual Sperm Egg Zygote Genetic Disorder

I A B XO R

II C D E Klinefelter Syndrome

III F G YO -

TABLE 1 [1 mark]
(a) What causes the abnormalities shown in TABLE 1?

Non-disjunction//homologous chromosomes fail to separate

(b) What is the genotype represented by E? [1 mark]
XXY

(c) Name genetic disorder R. [1 mark]
Turner syndrome

(d) (i) Explain how the zygote with genotype YO is produced. [2 marks]

The ovum produced do not carry any sex/X chromosomel/Abnormal
female gamete with genotype 22 +0
The abnormal ovum is fertilized by a sperm carrying the Y chromosomes

(ii) What would happen to the zygote with genotype YO? [1 mark]
Zygote fails to develop//dies//non-viable//lethal

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(e) Give TWO differences between the individual with genetic disorder R and the individual

with Klinefelter syndrome. [4 marks]

The genotype of R is XO while Klinefelter syndrome is XXY.

R is female while Klinefelter is male.

R is an example of monosomy/2n-1 while Klinefelter syndrome is an example of
trisomy/2n+1.

2 (a) FIGURE 2.1 shows types of small scale mutations that affect mRNA and amino
acids sequences.

Wild type mRNA 5’ GCU GGA GCA CCA GGA CAA GAU GGA 3’

Ala Gly Ala Pro Gly Gln Asp Gly

Silent mutation 5’ GCU GGA GCC CCA GGA CAA GAU GGA 3’
Mutation I Ala Gly Ala Pro Gly Gln Asp Gly

5’ GCU GGA GCA CCA AGA CAA GAU GGA 3’
Ala Gly Ala Pro Arg Gln Asp Gly

Mutation II 5’ GCU GGA GCA CCA GGA UAA GAU GGA 3’
Mutation III Ala Gly Ala Pro Gly

5’ GCU GGA GCC ACC AGG ACA AGA UGG 3’

Ala Gly Ala Thr Arg Thr Arg Trp

FIGURE 2.1

(i) Identify gene mutations I,II and III. [3 marks]

Mutation I : Missense mutation / base substitution
Mutation II : Nonsense mutation / base substitution
Mutation III : Frameshift mutation / base addition / base deletion

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(ii) Among mutations I, II and III, which is the least severe? Give a reason.
[2 marks]

Mutation I
It only changes one amino acid

(iii) Give two (2) differences between mutation I and mutation II. [2 marks]

Mutation I Mutation III
Involves one codons//Involves one amino Involves many codons//Involves
many amino acid
acid Involves base insertion//
Involves base substitution// Involves frameshift mutation
Does not involves frameshift mutation

(a) FIGURE 2.2 shows normal and mutation sequences of haemoglobin.

Normal haemoglobin 5’ACU CCU GAG GAA 3’

Mutated haemoglobin Thr Pro Glu Glu
5’ACU CCU GUG GAA 3’

Thr Pro Val Glu

FIGURE 2.2

(i) Name the disease caused by the mutation FIGURE 2.2 [1 mark]
Sicle cell anemia

(ii) The heterozygous gene for mutated haemoglobin above is resistant to

malaria. Give your reasons. [2 marks]

Heterozygous individuals produced both normal and sickle cell

Plasmodium malaria parasites cannot thrive/ survive in abnormal/sickle

cell haemoglobin/HB

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3. (a) FIGURE 3.1 shows mutation at a codon in a gene coding for β-globin.

FIGURE 3.1

(i) Name and define the gene mutation shown above. [2 marks]

Base substitution

Replacement of one (pair of) nucleotide with other (pair of)

nucleotides

(ii) What is the effect of gene mutation in FIGURE 6.1? [2 marks]

Causes missense mutation

In DNA, T is replaced with A// mRNA has GUA instead of GAA//

Glutamic acid/ Glu is replaced with valine/ Val

(iii) State one effect of mutant β-globin. [1 mark]

Red blood cells become sickled shape

Red blood cells have reduced ability to carry O2// O2 transport Any 1

not effective// sickle cell anaemia

(b) FIGURE 3.2 shows formation of polyploidy in plants.

FIGURE 3.2
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(i) Why is plant C sterile? [1 mark]

No (pairing of) homologous chromosomes// unable to undergo

synapsis/meiosis

(ii) Suggest how sterile plant C can reproduce. [1 mark]
Vegetative/ asexual reproduction

(iii)How does process X produce fertile offspring? [2 marks]

Chromosome doubling/ duplication

Non-disjunction occurs to all chromosomes (during mitosis)

(iv)Describe the reproductive characters of plant D. [3 marks]

Have homologous chromosomes// able to undergo synapsis/meiosis

Number of chromosomes is 32// 2n=32

Able to reproduce by sexual reproduction // able to produce gamete

(v) Apart from the process shown in FIGURE 3.2, suggest another method on

how plant D can be formed. [1 mark]

Union of unreduced gametes of plant A and B

4. (a) FIGURE 4.1 shows the types of chromosomal aberration.

FIGURE 4.1
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(i) Define chromosomal aberration. [1 mark]
A change in chromosome structure

(ii) Identify chromosomal aberration S and T. [2 marks]
S : Inversion
T : Translocation / Interchromosomal translocation

(iii) State two (2) differences between chromosomal aberration S and T.
[2 marks]

S T 1/0

A segment/piece of a Involves a region of a 1/0
chromosome breaks off and chromosome breaking off and 1/0
reattcahes in reverse order (180o rejoining to a non-homologous
from the original orientation)
chromosome
Pericentric inversion
Reciprocal / non-Robertsonian /
Involves 1 chromosome interchromosomal translocation

Involves 2 chromosomes

(b) FIGURE 4.2 shows the karyotypes of two individuals suffering from genetic
disorders.

FIGURE 4.2
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(i) Name the genetic disorder for individual A and B. [2 marks]
A : Klinefelter syndrome
B : Turner syndrome

(ii) Give three (3) characteristics of individual B. [3 marks]

• Infertility / sterile

• Short stature

• Webbed neck

• Triangular face

• Amenorrhoea / lack of menstruation

• Underdeveloped secondary female sexual characteristic / ovary /
breast

(iii) How does the genetic disorder in individual A occur? [3 marks]

• Non-disjunction of sex chromosome during oogenesis / meiosis
in female

• Produces (abnormal) ovum / female gamete that has genotype
22+XX / with an extra X chromosome

• Fertilisation of this (abnormal) ovum/ female gamete with normal
sperm / male gamete, 22+Y

OR

• Non-disjunction of sex chromosome during spermatogenesis /
meiosis in male

• Produces (abnormal) sperm / male gamete that has genotype
22+XY / with an extra X chromosome

• Fertilisation of this (abnormal) sperm / male gamete with normal
ovum / female gamete, 22+X

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5. a) Discuss non-disjunction involving sex chromosomes in women and its consequences
[10 marks]

No Answers
1 Women carry two X chromosomes //XX chromosomes
2 When sex chromosomes fails to separate during meiosis
3 Some of the gametes received both X chromosomes, known as XX gametes
4 The other gametes have no sex chromosomes, known as O gametes
5 When an XX gamete combine with Y gamete during fertilization, results in XXY zygote
6 This condition called Klinefelter syndrome
7 When an XX gamete combine with X gamete during fertilization, results in XXX zygote
8 This condition called metafemale/normal XXX/ Triple X/ Trisomy X/ superfemale
9 When O gamete fused with X gamete, produce XO zygote
10 This condition called Turner syndrome
11 When O gametes fused with Y gamete
12 Produced a (fatal) YO zygote

5. b) Explain inversion and translocation as types of chromosomal aberration and their

significance [10 marks]

No Answers
Inversion

1 Occurs when a chromosome segment breaks and reattached in the opposite orientation/
180° with respect to the rest of the chromosome

2 Two types of inversion that are perincentric and paracentric
3 Pericentric inversion include centromere during mutation
4 Paracentric inversion does not include centromeres during mutation
5 There is no change in genotype
6 But phenotype maybe changes
7 Also known as the position effects

Maximum : 5 marks
Translocation
8 When a chromosome segment breaks and reattached to another part of the same or other
chromosome
9 Simple translocation-chromosome segment translocate to another region of the same
chromosome/another chromosome// interchromosomal translocation-segment of one
chromosome translocate to another chromosome// intrachromosomal translocation-segment
of one chromosome translocate to another region of the same chromosome
10 Reciprocal translocation-exchanges of segment between two chromosome
11 Changes in position of the genes involved
12 There is no gain or loss of genetic materials// no changes in genotype// phenotype may
changes// phenotype may abnormal
13 Interchromosomal/ reciprocal translocation can change the linkage group

Maximum : 5 marks

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6 (a) Describe spontaneous mutation and induced mutation. [8 marks]

Spontaneous mutations
1. Occur naturally /Without human intervention
2. Caused by non-disjunction
3. Due to mutagens in the environment
4. These mutagens include cosmic rays, radioactive compounds, heat
5. Occur during DNA replication/repair /recombination

Induced mutation
6. Artificially induced/ Involve human intervention
7. Caused by mutagens
8. Physical agents / X-rays / UV-rays/ a/ β/ γ-rays.
9. Chemical agents Mustard gas, Ethylene amine/Colchicine/Ethyl-methyl sulphonate

(EMS)
10. It helps evolution /more genetic variations/Occur at higher rates/more rapidly

(b) Differentiate between Klinefelter syndrome and Turner syndrome. [12 marks]

Klinefelter syndrome Turner syndrome
Trisomy/2n+1 Monosomy /2n-1
Male individual Female individual
Genotype XXY Genotype XO
Individual has 47 chromosomes/ 44 + XXY Individual has 45 /44+X
Undeveloped testes Undeveloped ovary
Tall/enlarged breasts/feminized voice /knocked Short stature /poorly developed breasts/
knees/long limbs webbed neck

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