Genetic diversity and mutationAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Genetic diversity and mutation topic test

Total 54 marks

Name

Class

Date

1
In many people with cystic fibrosis, the CFTR gene has lost three consecutive bases. The polypeptide made from the mutant gene has 1479 amino acids instead of 1480, and its other amino acids are in the normal order.
(a)
Which type of gene mutation has occurred in the CFTR gene?
[1 mark]
ABase substitution
BBase deletion
CChromosome non-disjunction
DBase insertion that adds a codon
(b)
Why are the other amino acids in the polypeptide still in the normal order?
[1 mark]
AThe genetic code is universal
BThe deleted bases were all in an intron
CThe loss of exactly three bases removed one whole codon and kept the grouping of the remaining bases into triplets
DThe loss of three bases was reversed during translation
(c)
The mutation arose spontaneously in an ancestor. State when spontaneous gene mutations arise, and describe how a mutagenic agent changes the likelihood of gene mutation.
[2 marks]
Total for question 1: 4 marks
2
A zebrafish body cell contains 50 chromosomes. Before meiosis, the DNA in a cell in the ovary is replicated.
(a)
How many chromosomes are in each cell at the end of the first meiotic division?
[1 mark]
A25
B50
C100
D12
(b)
Which row describes the cells formed at the end of the second meiotic division?
[1 mark]
AFour diploid cells that are genetically identical
BTwo diploid cells that are genetically different
CFour haploid cells that are genetically identical
DFour haploid cells that are genetically different
(c)
Explain how the first division of meiosis halves the number of chromosomes in the daughter cells.
[2 marks]
Total for question 2: 4 marks
3
A species of frog has 26 chromosomes in each body cell, arranged as 13 pairs of homologous chromosomes. Assume that crossing over does not occur.
(a)
Calculate the number of different combinations of chromosomes that could be present in the gametes of one frog, and explain how independent segregation produces this variation.
[3 marks]
(b)
Calculate the number of different combinations of chromosomes possible in a zygote formed by random fertilisation of two gametes from different frogs, and explain why random fertilisation increases genetic variation. State one other process, not included in your calculation, that would increase variation further.
[4 marks]
Total for question 3: 7 marks
4
A baby boy has Klinefelter syndrome. Each of his body cells has 47 chromosomes, including three sex chromosomes, XXY. Tests showed that the extra X chromosome came from his mother, whose egg cells normally contain 23 chromosomes.
(a)
Explain how an error in meiosis in the mother could have produced an egg cell that led to this boy's chromosome number.
[6 marks]
(b)
Explain why egg cells must be made by meiosis and not by mitosis, and describe how meiosis produces genetically different egg cells.
[6 marks]
Total for question 4: 12 marks
5
Cells in a culture were exposed to X-rays. The rate of gene mutation in the cells rose sharply, and some cells were found to have base substitutions and others to have base deletions.
(a)
Which term describes the X-rays in this investigation?
[1 mark]
AA spontaneous mutation
BChromosome non-disjunction
CA degenerate code
DA mutagenic agent
(b)
Why do some base substitutions not change the amino acid sequence of a polypeptide?
[1 mark]
ASubstituted bases are always in introns
BMore than one codon can code for the same amino acid
CSubstitutions are repaired before translation
DSubstitutions never alter mRNA codons
(c)
Explain why a base deletion is usually more likely than a base substitution to change many amino acids in a polypeptide.
[2 marks]
Total for question 5: 4 marks
6
An onion plant has 16 chromosomes in each root cell. Its pollen grains are produced in the anthers and each pollen grain nucleus contains 8 chromosomes.
(a)
Which row describes the result of one division of a root tip cell?
[1 mark]
AMitosis; two cells each with 16 chromosomes
BMitosis; four cells each with 8 chromosomes
CMeiosis; two cells each with 16 chromosomes
DMeiosis; four cells each with 8 chromosomes
(b)
Which process produces the pollen nuclei with 8 chromosomes from diploid cells in the anther?
[1 mark]
AMitosis, because the number of cells increases
BFertilisation, because two nuclei fuse
CMeiosis, because the chromosome number is halved
DNon-disjunction, because chromosomes fail to separate
(c)
Explain why the pollen grains from one anther are genetically different from each other, whereas the cells of a root tip are genetically identical.
[2 marks]
Total for question 6: 4 marks
7
A diploid cell has four chromosomes: a long pair and a short pair. The cell is heterozygous at a gene on the long pair (alleles A and a) and heterozygous at a gene on the short pair (alleles B and b). Assume that crossing over does not occur.
(a)
Describe the chromosome content of the cells at the end of the first and the second meiotic division.
[3 marks]
(b)
State the combinations of alleles that the gametes could contain, and calculate the number of different pairings of gametes that are possible when a gamete from one such cell fuses at random with a gamete from another cell of the same genotype. Explain your answer.
[4 marks]
Total for question 7: 7 marks
8
In a fungus, the body is made of haploid cells, each with 7 chromosomes. Two haploid nuclei from different individuals fuse to form a diploid zygote nucleus. The zygote nucleus then immediately divides to form four haploid nuclei, each of which becomes a spore. A spore germinates and grows into a new body by repeated cell division. In one cross, one set of four spores was found to contain 8, 8, 6 and 6 chromosomes.
(a)
Identify where meiosis occurs in this life cycle, and explain how the life cycle produces genetic variation.
[6 marks]
(b)
Explain how the set of spores containing 8, 8, 6 and 6 chromosomes could have been produced.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).