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In one species of squirrel, Sciurus carolinensis, fur colour is controlled by one gene, with two codominant alleles - AQA - A-Level Biology - Question 1 - 2021 - Paper 1
Question 1
In one species of squirrel, Sciurus carolinensis, fur colour is controlled by one gene, with two codominant alleles. C^G represents the allele for grey fur colour, a... show full transcript
Worked Solution & Example Answer:In one species of squirrel, Sciurus carolinensis, fur colour is controlled by one gene, with two codominant alleles - AQA - A-Level Biology - Question 1 - 2021 - Paper 1
Step 1
Use the Hardy-Weinberg equation to estimate how many squirrels had brown-black fur.
Answer
To use the Hardy-Weinberg principle, we start by defining the allele frequencies. Let p represent the frequency of the C^G allele and q the frequency of the C^B allele. Since 2 out of 34 squirrels had black fur (C^B C^B), we can determine the frequency of the black fur genotype as follows:
Next, calculate q:
To find p, use the relationship p + q = 1:
The squirrels with brown-black fur (C^G C^B) are represented by 2pq:
Thus, the estimated number of squirrels with brown-black fur is:
$$2pq * 34 \approx 12.49 ext{ squirrels} \approx 12.$
Step 2
Calculate the actual frequency of the C^G allele.
Answer
Given that there are 16 squirrels with brown-black fur (C^G C^B), we can use this count along with the total population of 34 to find the actual frequency of the C^G allele:
Let x be the number of C^G alleles:
The population consists of:
- 2 squirrels with black fur (C^B C^B) - 2 alleles of C^B
- 16 squirrels with brown-black fur (C^G C^B) - 16 C^G and 16 C^B alleles
Calculating the total number of alleles:
Total alleles = 34 * 2 = 68
Now, count the total C^G alleles:
Total C^G alleles = 16 (from C^G C^B squirrels) + 0 (from C^B C^B squirrels) = 16
Then, calculate the frequency of C^G:
or 0.24 when rounded to 2 decimal places.
Step 3
D. The phenotypic variation shown in S. carolinensis and other closely related species is caused by genetic drift.
Answer
The available data indicates that the genotypic and phenotypic variations in S. carolinensis from North America and the UK are identical. Since the mutation causing black fur is also seen in closely related species, it implies that these characteristics are inherited from a common ancestor rather than due to independent mutations or genetic drift.
Step 4
Calculate the percentage reduction in size of the protein coded for by the C^B allele.
Answer
To calculate the percentage reduction in size, we determine the difference in length between the two proteins:
Given:
- Length of protein coded for by C^B allele = 306 amino acids
- Length of protein coded for by C^G allele = 8/306 * 100 (from the marking scheme's clue, assumes this ratio means the full length of C^G is now editable)
Now, say the protein coded for by C^G is 942 amino acids long. Thus:
Percentage reduction = \frac{(942 - 306)}{942} * 100\approx 67.5%.
Rounded to three significant figures: 67.5%.