Comprehension (A Level only) (AQA A Level Biology)

Suggest why more than one person was used for the creation of the reference sequences (lines 11 - 16).

Describe how some base substitutions in the DNA sequence of a gene can be harmless while others can lead to disease through altered protein-protein interactions (lines 20 - 23).

The cancer cells within a particular patient were found to be caused by the known overexpression of a specific gene. Suggest and explain how a medical cancer treatment could be tailored to the individual (lines 29 - 33).

The sequencing machines can sequence 80,000 bases in 1 second. (lines 9 -11) If the human genome is 6,200 megabase pairs long, how much time will it take to sequence a whole human genome. 1 megabase pairs = 1,000,000 base pairs. Give your answer in hours.

Some of the patients with cancer exhibited zero differences or variation in their genomes from the reference genome. One of the researchers suggested that there could be important differences in their epigenomes. Explain what an epigenome is and suggest how epigenetic changes could cause cells to become cancerous.

Genome sequencing can be used to sequence the genomes of disease-causing viruses and bacteria. Suggest how the genomic information obtained about these organisms could be applied in human medicine.

Explain how genetic fingerprinting would allow scientists to identify the mother and father of an adolescent Amur leopard that had been released into the wild.

Explain why genetic variation within a wild population is important. Suggest how DNA fingerprints could be used to help maintain genetic variation within the captive Amur leopard population.

i) Suggest two different types of body cells from the Amur leopards that could have been present in their faeces samples. The named cells must contain DNA (lines 13 - 15).

ii) Explain the effect of PCR (lines 15 -17).

Explain why the primers used bind solely to Amur leopard DNA, and not to the DNA from other organisms present in the faeces (lines 13 - 16).

Blood or tissue samples can also be used to obtain DNA from Amur leopards. Suggest a disadvantage of using a blood or tissue sample to obtain DNA from Amur leopards.

12% of the population on the small island near New Zealand are affected by total colour blindness (lines 9–11) 

Use the information provided to calculate how many more times an individual on the island is likely to have total colour blindness compared to an individual living elsewhere. Show your working.

Red-green colour blindness affects more men than women but blue-yellow colour blindness affects men and women equally (lines 12–13 and lines 16 -19). Explain why.

People with red-green and blue-yellow colour blindness are unable to distinguish between other colours as well. (lines 12–19). Explain why.

Some of the recent research into the treatment of red-green colour blindness involves the use of gene therapy (lines 20 - 25). Suggest how gene therapy cells could correct red-green colour blindness.

The use of induced pluripotent stem cells (iPS cells) could prove a more successful method than gene therapy for the correction of red-green colour blindness (lines 26–27). Using the information provided, suggest and explain two reasons why.

Two couples, couple X and couple Y, used a genetic screening service to find out if they were likely to pass on any harmful alleles to their potential children. The genomes of all four individuals were sequenced and any harmful mutations identified. None of the parents showed signs or symptoms of MD.

The results revealed the following:

• Couple X had a 25% probability of their children having

• Couple Y had a 100% probability of their children having

Using your knowledge of inheritance and the information in lines 6–10, explain the results of couple X and couple Y.

A small amount of DNA was extracted from the couples mitochondrial and nuclear DNA. PCR was carried out before sequencing. 

i) Suggest why PCR was used.

ii) Explain how sequencing would allow for mutations to be identified.

Suggest how altering the anticodon of a tRNA results in MD (lines 10–13).

The post-exercise blood lactate concentration of an individual with MD is often much greater than the normal range (line 16). Suggest why.