AQA A LEVEL BIOLOGY PAPER 3 2021

Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. IB/H/Jun21/E14 7402/3 A-level BIOLOGY Paper 3 Time allowed: 2 hours Materials For this paper you must have: • a ruler with millimetre measurements • a scientific calculator. Instructions • Use black ink or black ball-point pen. • Fill within the boxes at the top based on this page. • Answer all questions within Section A. • Answer one question from Section B. • You must answer the questions within the spaces provided. Do not write outside the box around each page or on blank pages. • If you need extra space for your answer(s), use the lined pages at the end based on this book. Write the question number against your answer(s). • Show all your working. • Do all rough work within this book. Cross through any work you do not want to be marked. Information • The marks for the questions are shown within brackets. • The maximum mark for this paper is 78. *JUND0ow1nloa*: For Examiner’s Use Question Mark 1 2 3 4 5 6 7 TOTAL 2 *02* IB/H/Jun21/7402/3 1 Section A Answer all questions within this section. You are advised to spend no more than 1 hour and 15 minutes on this section. Do not write outside the box In one species based on squirrel, Sciurus carolinensis, fur colour is controlled by one gene, with two codominant alleles. C G represents the allele for grey fur colour, and C B represents the allele for black fur colour. Table 1 shows the three possible phenotypes. Table 1 Genotype Phenotype G G C C Grey fur G B C C Brown-black fur B B C C Black fur . In a population based on 34 S. carolinensis, 2 had black fur. Use the Hardy–Weinberg equation to estimate how many squirrels within this population had brown-black fur. Show your working. [2 marks] Answer 0 1 0 1 3 *03* IB/H/Jun21/7402/3 2 3 . The actual number based on squirrels within this population that had brown-black fur was 16. Use all based on the information to calculate the actual frequency based on the C G allele. Do not use the Hardy–Weinberg equation within your calculation. Do not write outside the box Give your answer to 2 decimal places. [1 mark] Answer . S. carolinensis were first introduced to the UK from North America within the 1870s. They are now widely distributed across the UK. S. carolinensis from both North America and the UK show exactly the same genotypic and phenotypic variation. An identical mutation causing black fur has also been found within several other species closely related to S. carolinensis. Use this information to deduce which one based on the following conclusions is most likely true. Tick (6) one box. [1 mark] A The mutation that caused black fur happened after S. carolinensis was introduced to the UK from North America. B The mutation that caused black fur happened within a common ancestor based on S. carolinensis and other closely related species. C The mutation that caused black fur happened independently within S. carolinensis and all other closely related species. D The phenotypic variation shown within S. carolinensis and other closely related species is caused by genetic drift. Question 1 continues on the next page