AQA GCSE Biology 8461: Inheritance, variation and evolution – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover topic 6, Inheritance, variation and evolution (sections 4.6.1–4.6.4), of the AQA GCSE Biology (8461) specification, for teaching from September 2016 and exams from 2018 onwards. The topic is examined on Paper 2, set at Foundation and Higher tier. Parts labelled (Higher tier only) test content the specification marks “(HT only)”; Foundation candidates can skip them.

Learn the content first in the study guide and the revision notes. The course hub is AQA GCSE Biology, and the printable checklist lists every statement.

Questions

1. Describe how meiosis produces gametes from a cell in the testes. [3]

2. Explain what is meant by each term.

(a) Allele [1] (b) Heterozygous [1] (c) Phenotype [1]

3. In mice, grey fur (G) is dominant to white fur (g). Two heterozygous grey mice are bred several times and produce 58 grey and 19 white offspring.

(a) Calculate the ratio of grey to white offspring in the form n : 1. Give n to 2 decimal places. [1] (b) Suggest why the ratio is not exactly 3 : 1. [1] (c) (Higher tier only) A heterozygous grey mouse is crossed with a white mouse. Construct a Punnett square and predict how many of 40 offspring would be white. [4]

4. Polydactyly is caused by a dominant allele, D. A man with polydactyly (Dd) has children with a woman who does not have it. Use a genetic diagram to find the probability that a child has polydactyly. [3]

5. Cystic fibrosis is caused by a recessive allele, f.

(a) Explain how two parents without cystic fibrosis can have a child with the disorder. [3] (b) State the probability that their next child is a carrier. [1] (c) Embryo screening can detect cystic fibrosis. Give two arguments for and two arguments against embryo screening. [4]

6. A section of one DNA strand has the base sequence TACGGATTC.

(a) (Higher tier only) Write the sequence of the complementary strand. [1] (b) A gene is 1236 bases long. Calculate the number of amino acids in the protein it codes for. [1] (c) (Higher tier only) Explain how a mutation in a gene could stop an enzyme from working. [3]

7. Use a genetic diagram to show that there is an equal chance of a baby being a boy or a girl. [3]

8. A hospital tests 300 samples of a bacterium each year for resistance to an antibiotic. In the first year 12 samples are resistant. Ten years later 66 samples are resistant.

(a) Calculate the percentage of samples that were resistant in each year. [2] (b) Explain how the population of resistant bacteria increased. [4] (c) Give two ways doctors or patients can reduce the development of resistant strains. [2]

9. A farmer wants a variety of wheat that is resistant to a fungal disease.

(a) Describe how she could produce this variety by selective breeding. [4] (b) Give one risk of selective breeding. [1]

10.

(a) (Higher tier only) Describe the main steps used to genetically engineer bacteria to make human insulin. [4] (b) Give one concern some people have about GM crops. [1]

11. Describe how adult cell cloning is used to produce a cloned animal, and explain why the clone is genetically identical to the adult that gave the body cell. [5]

12.

(a) Give three reasons why Darwin’s theory of evolution by natural selection was only gradually accepted. [3] (b) Explain how Lamarck’s idea about inheritance differs from Darwin’s. [2] (c) Give two reasons why the fossil record is incomplete. [2] (d) Name the three domains in Woese’s classification system. [1] (e) The lion’s scientific name is Panthera leo. State which part of the name is the genus. [1]

Answers

1. Copies of the genetic information are made [1]; the cell divides twice to form four gametes [1]; each gamete has a single set of chromosomes and all are genetically different [1] Examiner insight: “The cell divides into two identical cells” describes mitosis and is a contradiction; it cancels the division mark.

2. (a) A different form of the same gene [1] (b) The two alleles of a gene are different [1] (c) The characteristic that is expressed (produced by the genotype) [1] Examiner insight: Definitions must be precise; “a gene that is different” for allele is too vague for the mark.

3. (a) 58 ÷ 19 = 3.05 : 1 [1] (b) Fertilisation is random, so real numbers vary from the expected ratio (the sample is small) [1] (c) Parent genotypes Gg × gg [1]; gametes G and g from one parent, g only from the other [1]; Punnett square gives Gg, Gg, gg, gg, so 1 : 1 (probability of white = 1/2) [1]; expected white = 40 × 1/2 = 20 [1] Examiner insight: In (c) the gametes must be shown separately; a square with no gametes loses that marking point even if the offspring are right.

4. Parents Dd × dd, gametes D, d and d [1]; offspring Dd, Dd, dd, dd [1]; probability = 1/2 (50%) [1] [3] Examiner insight: A probability written as “1 : 1” is a ratio, not a probability; the final mark needs 1/2, 0.5 or 50%.

5. (a) Both parents are heterozygous (carriers, Ff) [1]; each can pass on the recessive allele f [1]; a child who inherits f from both parents (ff) has cystic fibrosis [1] (b) 1/2 [1] (c) For: parents can make an informed decision [1]; reduces suffering from the disorder (or reduces long-term treatment costs) [1]. Against: the procedure is expensive or may harm the embryo [1]; ethical concern about destroying embryos or selecting characteristics [1] Examiner insight: Arguments must be distinct; “it is wrong” and “it is unethical” count as one point, so two against-marks need two different ideas.

6. (a) ATGCCTAAG [1] (b) 1236 ÷ 3 = 412 [1] (c) A change in the base sequence changes the amino acid sequence [1]; the protein folds into a different shape [1]; the active site no longer fits the substrate, so the enzyme cannot work [1] Examiner insight: In (c) the marks follow a chain: bases → amino acids → shape → active site. Skipping straight to “the enzyme is denatured” is wrong and scores nothing.

7. Mother XX, father XY [1]; gametes X, X and X, Y combined in a Punnett square to give XX, XX, XY, XY [1]; 2 girls : 2 boys, so probability of a boy = 1/2 [1] [3] Examiner insight: A diagram with no statement of the outcome loses the last mark; finish with the ratio or probability in words.

8. (a) 12 ÷ 300 × 100 = 4% [1]; 66 ÷ 300 × 100 = 22% [1] (b) A mutation produced a resistant strain [1]; the antibiotic kills non-resistant bacteria [1]; resistant bacteria survive and reproduce [1]; bacteria reproduce quickly, so the resistant strain spreads and becomes a larger proportion [1] (c) Do not prescribe antibiotics for viral or non-serious infections [1]; patients complete the full course [1] Examiner insight: Saying the antibiotic “causes” the mutation or bacteria “become immune” is a contradiction and caps (b); the mutation happens first, by chance.

9. (a) Choose parent plants that show the most resistance [1]; breed them together [1]; select the offspring with the best resistance and breed them [1]; repeat over many generations until all offspring are resistant [1] (b) Inbreeding, making the variety prone to other diseases or inherited defects (reduced variation) [1] Examiner insight: “Repeat over many generations” is a separate marking point; answers that stop after one generation lose it.

10. (a) Enzymes are used to cut out (isolate) the human insulin gene [1]; the gene is inserted into a vector, a bacterial plasmid [1]; the plasmid carries the gene into bacterial cells [1]; the bacteria make human insulin, which is collected [1] (b) Effect on populations of wild flowers and insects (or effects of eating GM crops on health not fully explored) [1] Examiner insight: Name the vector; “the gene is put into the bacteria” without a plasmid or virus misses the vector mark.

11. The nucleus is removed from an unfertilised egg cell [1]; the nucleus from an adult body cell (e.g. skin cell) is inserted into the egg [1]; an electric shock stimulates the egg to divide to form an embryo [1]; the ball of cells is inserted into the womb of an adult female [1]; the embryo’s genetic information all comes from the body-cell nucleus, so it matches that adult [1] [5] Examiner insight: Saying the clone is identical to the egg donor or surrogate contradicts the method and loses the explanation mark.

12. (a) It challenged the idea that God made all animals and plants [1]; there was insufficient evidence at the time [1]; the mechanism of inheritance and variation was not known until 50 years later [1] (b) Lamarck: changes during an organism’s lifetime are inherited [1]; Darwin: variation already exists and the best-suited variants survive and pass on their characteristics [1] (c) Early forms of life were soft-bodied and left few traces [1]; traces were destroyed by geological activity [1] (d) Archaea, bacteria and eukaryota [1] (e) Panthera [1] Examiner insight: In (b) a comparison needs both sides; describing Lamarck alone earns only one mark.

Where marks are usually lost

• Saying meiosis gives two cells or identical cells.
• Punnett squares drawn without parent genotypes or gametes.
• Probabilities written as ratios, or ratios not simplified.
• Mixing up “carrier” (heterozygous) with “affected” (homozygous recessive).
• In DNA questions, pairing A with G or C with T.
• Saying an enzyme is “denatured” by a mutation instead of explaining the changed shape.
• Natural selection answers that say bacteria “adapt” or “become immune”.
• Selective breeding without “many generations”.
• Genetic engineering without naming enzymes or the vector.
• Adult cell cloning answers that swap the egg and body-cell roles.

Next steps

• Recap with the revision notes.
• Reread any weak section in the study guide.
• Browse other topics on the AQA GCSE Biology hub.
• Track coverage with the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

AQA GCSE Biology (8461) specification, Version 1.0 (21 April 2016), for teaching from September 2016 and exams from 2018 onwards, AQA – section 4.6, Inheritance, variation and evolution.