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1.
Figure 2 shows the cycle of a somatic cell.
S
G1
C
Daughter cells
G2
Nuclear
division
Figure 2
a) Define cell cycle.
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[1 mark]
b) (i) What is the longest phase in interphase?
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[1 mark]
(ii) State the events that occur in b) (i).
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[3 marks]
c) What happens during S phase? Give two significance of the phase.
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[3 marks]
d) (i) Name the process labelled C.
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[1 mark]
(ii) In animal cell, C involves the formation of cleavage furrow but not in plant
cell. Explain why?
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[1 mark]
2.
a) In human, cystic fibrosis is caused by a recessive allele, f, of a particular gene.
The albino condition, in which no melanin is produced in the skin, is determined
by a recessive allele, a, of another skin. These two genes are found on a different
chromosome.
(i)
What is meant by allele?
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[1 mark]
(ii)
An unaffected individual, who is heterozygous from both albinism and
cystic fibrosis can produce a range of gametes with respect to these two
genes. With reference to meiosis, describe how the difference in the
gametes can arise.
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[2 marks]
(iii)
Two individuals, heterozygous for albinism produce a child. Calculate the
probability that this child is albino.
[2 marks]
b) In cats, long hair is controlled by a dominant allele, L, while short hair is
controlled by its recessive allele, l. On the other hand, brown hair is controlled
by a dominant allele, B, while white hair is controlled by its recessive allele, b.
Based on the information given, answer the following questions:
(i)
Determine the expected phenotypic ratio among F1 progeny for the
cross between heterozygous cats.
[2 marks]
(ii)
What percentage of the F1 progenies in cross (i) is expected to be pure
breed?
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[1 mark]
(iii)
What percentage of F1 progenies in cross (i) can be used as a test cross
parent?
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[1 mark]
(iv)
What percentage of F1 progenies in cross (i) is expected to have short
and brown hair?
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[1 mark]
3.
Phenylketonuria (PKU) is a genetic diseases controlled by the recessive allele. It is
also an inborn error of phenylalanine metabolism and leads to severe mental
retardation.
Table 1 shows the number of the normal and the abnormal individuals in a
population.
YEAR
The number of the normal individuals
The number of the abnormal individuals (having (PKU)
Total
1995
4996
4
5000
2005
4992
8
5000
Table 1
a) (i)
Calculate the frequency of the recessive allele in 1995 and 2005.
[2 marks]
(ii)
Give the conclusion of the allele frequency at a (i).
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[1 mark]
(iii)
Give three assumptions to calculate the allele frequency.
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[3 marks]
4.
a)
(i)
State the Hardy-Weinberg principle.
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[2 marks]
(ii)
One of the condition for this principle to be achieved is large population
size. Explain why?
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[3 marks]
b)
In a randomly breeding population of mice, black coat (H) is dominant to white
coat (h). In the population, 36% have white coats.
Calculate the genotype frequencies of black coat mice in this population.
[2
c)
marks]
In a human population, the frequency of the recessive individuals for extra-long
eyelashes is 90 per 1000. What is the individual percentage of this population
that carries recessive allele but displays the phenotype of short eyelashes?
[3 marks]