AQA A Level Biology

Topic Questions

8.1 Genetic Mutations (A Level only)

1a1 mark

Give the meaning of the term mutation.

1b3 marks

Identify and describe three different types of mutation.

1c2 marks

Explain how a mutation may result in synthesis of a non-functional protein.

1d2 marks

Explain what is meant by the term silent mutation

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2a2 marks

List two examples of mutagenic agents.

2b1 mark

Carcinogenic factors are those which can cause cancer. Most carcinogens are also mutagenic agents, but there are a few that cause cancer in other ways.

State the effect that a factor must have on a cell in order to be considered carcinogenic.

2c2 marks

There are 3.2 x 109 base pairs in the human genome.

Assuming that mutations occur during DNA replication at an approximate rate of 1 in 1 x 106 base pairs, calculate the approximate number of mutations that would occur if the entire genome was to be replicated. Give your answer in standard form.

2d1 mark

State why it is not possible to predict where or when a mutation is likely to occur during DNA replication.

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3a2 marks

The specific location of a mutation determines the severity of the impact on the resulting protein. During protein synthesis, a deletion mutation occurs which removes the second nucleotide base of the sequence.

Suggest why this mutation is likely to have a more significant impact on the resulting protein than a deletion mutation which occurs towards the end of the sequence. 

3b2 marks

Identify and explain the feature of the genetic code which allows a silent mutation to occur.

3c2 marks

Suggest why a translocation mutation is likely to have a bigger impact than a substitution mutation.

3d1 mark

Table 1 shows an original DNA base sequence alongside the copied base sequence which shows a mutation.

Table 1

Original DNA base sequence

C

A

G

T

T

C

G

C

T

A

C

G

Mutated DNA base sequence

C

A

G

T

T

C

C

C

T

A

C

G

Identify the type of mutation shown in this section of DNA.

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4a2 marks

A nonsense mutation results in the formation of one of the three following triplet codes: UGA, UAG or UAA.

Table 1 shows the variations of the triplet code and what they code for.

Table 1

figure-4

Use the information from Table 1 and your own knowledge to explain the effect that a nonsense mutation would have on the resulting protein.

4b2 marks

Human DNA is made up of introns and exons.

State why mutations that occur in the introns during protein synthesis will have no impact on the resulting protein.

4c2 marks

State and explain which stage of the cell cycle mutations are most likely to occur.

4d3 marks

Tumour suppressor genes are a group of genes that can code for proteins that prevent cell division.

Explain how a mutation within this type of gene could lead to cancer

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5a1 mark

State one environmental influence which could cause a mutation in DNA.

5b1 mark

The Philadelphia chromosome is a mutated version of chromosome 22, found to contain a gene usually found on chromosome 9 called the ABL gene. 

Figure 1

figure-5

Use your knowledge of mutation and Figure 1 to suggest the type of mutation which leads to the formation of the Philadelphia chromosome.

5c3 marks

State how the mutation described in part b) leads to the formation of a new protein.

5d2 marks

Table 1 and Table 2 contain information about a base sequence and the triplet code.

Table 1

Original DNA base sequence

A

T

T

G

G

C

G

T

G

T

C

T

Amino acid sequence

Ile

Gly

Val

Ser

Mutation 1 DNA base sequence

A

T

T

G

G

A

G

T

G

T

C

T

Table 2

DNA triplets

Amino acid

GGT, GGC, GGA, GGG

Gly

GTT, GTA, GTG, GTC

Val

ATC, ATT, ATA

Ile

TCC, TCT, TCA, TCG

Ser

CTC, CTT, CTA, CTG

Leu

Use the information in Table 2 to describe and explain how mutation 1 in Table 1 alters the resulting sequence of amino acids.

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1a3 marks

Explain why the effect of a substitution mutation may have less of an impact than a deletion mutation.

1b2 marks

Identify the type of mutation that would result in the protein formed in Figure 1

figure-1

1c3 marks

Cystic fibrosis is a mutation caused by the deletion of one amino acid from the CFTR protein. The CFTR protein forms a channel which moves negatively charged chloride ions across the cell membrane. Cystic fibrosis sufferers lack these CFTR channels which means chloride ions cannot be transported out of the cell.

A symptom of cystic fibrosis is the production of thick sticky mucus, which blocks airways and causes persistent coughing. Increased mucus also increases susceptibility to infections of the lung.

Explain how this mutation to the CFTR gene would lead to a cystic fibrosis sufferer lacking effective CFTR protein channels.

1d4 marks

With reference to water potential gradients, suggest how a mutation of the CFTR gene may lead to the symptoms described in part (c). 

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2a3 marks

Identify the type of mutation shown in Figure 1 and explain its effect on the resulting protein.

Figure 1

figure-2

2b4 marks

A study was completed to compare cigarette consumption to death rates due to lung cancer amongst males and females from 1900 to 2010. The results of this study are represented in the graph in Figure 2. 

Figure 2

figure-3

The scientist concluded that cigarette consumption was a key factor influencing death rates due to lung cancer over this period. Use Figure 2 to evaluate this claim.

2c2 marks

In a second study, it was found that, on average, there is one DNA mutation per lung cell for every 50 cigarettes smoked. 

The analysis found that people who smoke a pack of 20 a day for a year generate 160 mutations per lung cell, 110 per larynx cell, 45 per pharynx cell, 25 per bladder cell and 5 per liver cell.

Calculate the number of mutations a person would experience per year if they reduced the number of cigarettes they smoked by 20%.

2d3 marks

Explain how a carcinogen, such as tobacco, can lead to the formation of lung cancers.

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3a2 marks

Explain why the degeneracy of the genetic code might provide an advantage to organisms.

3b2 marks

Look at the base codes in Table 1 and identify the type of mutation shown on the mRNA, provide an explanation for your choice.

Table 1

DNA A T G C G T T C A T T T A A G
mRNA U A C G C A U G A A A A U U C

3c4 marks

Table 2 shows the different combinations of bases on the mRNA and the amino acids which they code for. The amino acid names have been abbreviated; for example, ‘Gly’ stands for the amino acid Glycine.

Table 2

EKcq2hx0_figure-4

Use Table 2 to explain what effect the mutation identified in part (b) would have on the protein formed.

3d2 marks

You have an RNA transcript that is 135 nucleotides long. A frameshift mutation occurs at the 101st nucleotide. 

Calculate the number of amino acids that will be correct?

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4a4 marks

The Philadelphia chromosome is a mutated version of chromosome 22, found to contain a gene usually found on chromosome 9 called the ABL gene. 

Figure 1

k6GjXBqn_figure-5

Identify the type of mutation which forms the Philadelphia chromosome and suggest why it may have a significant impact on the phenotype of the organism.

4b2 marks

The Philadelphia mutation creates a fusion gene which is a combination of the ABL gene from chromosome 9 and BCR gene from chromosome 22. This fusion gene is shown to increase activity of tyrosine kinase, an enzyme which is involved in the switching on and off of many cellular functions, including cell division.

Suggest how the Philadelphia mutation could result in the production of a large number of immature lymphocytes.

4c2 marks

In America, 0.5% of all cancer cases are diagnosed as acute lymphoblastic leukemia. 80% of those cases are in children. In 2019 there were 1,762,400 diagnosed cancer cases in America. 

Calculate the number of children diagnosed with acute lymphoblastic leukemia in 2019.

4d4 marks

Identify two mutagenic agents and explain how they might increase the occurrence of genetic mutations.

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1a3 marks

Sickle cell anemia is a disease caused by certain mutations of the gene coding for β-haemoglobin. Table 1 shows part of the DNA base sequence coding for β-haemoglobin and two mutations of this sequence.

Table 1

 

DNA base sequence coding for β-haemoglobin

                       
 

mRNA sequence for β-haemoglobin

A

C

U

C

C

U

G

A

G

G

A

G

 

DNA base sequence with mutation 1

                       
 

mRNA base sequence with mutation 1

A

C

U

C

C

U

G

U

G

G

A

G

 

DNA base sequence with mutation 2

                       
 

mRNA base sequence with mutation 2

A

C

U

C

C

U

G

A

A

G

A

G

Complete Table 1 with the DNA sequences that are transcribed to produce β-haemoglobin, mutant 1 and mutant 2.

1b5 marks

Table 2 shows some examples of amino acids, their structures and the mRNA codons that code for them. 

Table 2

ItvAFO3o_1

i)
Assuming that the sequence in Table 1 is given in-frame, state what type of mutations are seen in sickle cell anemia. 

ii)
Explain the effect of mutation 1 and mutation 2 on the protein that is produced in each case. 
1c2 marks

Sickle cell anemia causes aggregation of the mutated haemoglobin proteins which changes the shape of red blood cells, as seen in Figure 1, therefore affects red blood cell function. 

Figure 1

LHf_B0lu_2


State what function of the red blood cell would be affected by sickle cell anemia and explain why the shape of white blood cells is not affected by the disease. 

1d1 mark

One mutation causing sickle cell anemia was originally only found in one population in central Africa. It is now found in many different populations across Asia and Africa. Suggest how the spread of this mutation may have occurred.

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2a2 marks

FG syndrome is a rare genetic disorder caused by an inversion mutation in the MED12 gene on the X chromosome. FG syndrome is a recessive disorder that can cause a characteristic facial appearance, developmental delays and hyperactivity.

FG syndrome is more prevalent in males, suggest why.

2b2 marks

Describe what is meant by an inversion mutation.

2c3 marks

Suggest the effect of an inversion mutation on the functionality of the protein produced.

2d2 marks

Gene mutations occur spontaneously. State the part of the cell cycle when gene mutations are most likely to occur and give an explanation for your answer. 

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3a1 mark

The Mormon faith was founded in 1840 by Lynman Hinman. The mormon community are highly polygamous, with most men having at least three wives. 80% of the current population in Shortcreek, USA are blood descendants of the town’s founders Joseph Jessop and John Barlow. The community is also very secular with interbreeding only occurring within the community. 

One small Morman town in Hildale, Utah was recently reported to have 20 cases of a rare genetic condition caused by fumarase deficiency leading to severe neurological problems. The disease is recessive and extremely rare with the usual risk being 1 in 400 million. The risk of inheriting the disease in Utah is 1 in 500. 

Use the information provided to calculate the current Mormon population of Hildale, Utah. 

3b2 marks

The faulty allele that causes fumarase deficiency is the result of a mutation of a gene called FH. This mutation leads to the production of a protein that is missing one amino acid compared to individuals without the mutation.

Suggest how the mutation leads to the production of a protein that has one amino acid missing.

3c2 marks

Fumarase is an enzyme that converts fumarate (4C) into malate (4C) in the Kreb’s cycle. 

Suggest how producing a fumarase protein with one less amino acid may lead to a disease such as the one found in the Mormon community of Hilldale.

3d1 mark

Mutations such as the one seen in fumase deficient patients are usually caused by an error during DNA replication. Name the enzyme that is responsible for ensuring the DNA sequence is correct. 

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4a1 mark

Fetal haemoglobin is the dominant form of haemoglobin used and produced by a fetus as it grows within its mothers womb. Fetal haemoglobin is made from two alpha chains, the same as those in adult haemoglobin, and two gamma chains unique to this protein.

The genes for gamma and beta haemoglobin are both found close to each other on chromosome 11 in humans. Researchers sequenced the DNA coding for gamma and beta haemoglobin chains and found the sequences were very similar. Both the gamma and beta genes have 438 coding nucleotides. 

Calculate how many amino acids make up a beta or gamma chain.

4b4 marks

Originally humans only had one haemoglobin gene on chromosome 11. Suggest how a fetal version of the gene evolved.

4c4 marks

β-thalassemia is a genetic disease caused by a mutation in the beta haemoglobin gene. One of the causes of β-thalassemia is two adenine nucleotides being removed from codon 8 of the beta hemoglobin gene. One of the major effects of this deletion is that codon 21 changed from CAG to UAG.

 Figure 1

screenshot-2023-07-06-at-9-27-05-pm

Using Figure 1 and your knowledge of deletion mutations, suggest how this mutation affects the protein that is produced.

4d1 mark

For someone to suffer with β-thalassemia they must have two mutated beta haemoglobin alleles.

State the type of the genotype that causes the β-thalassemia phenotype.

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5a1 mark

There are several ways in which genes can become mutated.

Which statement(s) in Table 1 correctly describes the effect of a mutation in the exon of a gene.

Table 1

A

A substitution always results in a change to the encoded amino acid.

B

An addition may change more than one amino acid.

C

An inversion will result in a change in the number of DNA bases.

D

A deletion will not result in a frame shift.

5b1 mark

Chronic myeloid leukemia (CML) is a type of cancer that affects white blood cells. CML is caused when a section of chromosome 9 breaks off and fuses with chromosome 22.

Name the type of mutation that occurs in chronic myeloid leukemia.

5c2 marks

A type of malignant tumour cell divides every 6 hours.

Starting with one malignant tumour cell, and assuming none die, how many tumour cells will be present after 8 weeks?

Give your answer in standard form.

5d3 marks

Give three factors that increase the chances of genetic mutation.

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