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In a population of 34 S - AQA - A-Level Biology - Question 1 - 2021 - Paper 3
Question 1
In a population of 34 S. carolinensis, 2 had black fur. Use the Hardy-Weinberg equation to estimate how many squirrels in this population had brown-black fur. Show y... show full transcript
Worked Solution & Example Answer:In a population of 34 S - AQA - A-Level Biology - Question 1 - 2021 - Paper 3
Step 1
Use the Hardy-Weinberg equation to estimate how many squirrels in this population had brown-black fur.
Answer
To find the number of squirrels with brown-black fur, we first determine the total number of squirrels with either black fur or brown-black fur:
Number with black fur (given) = 2 Number with brown-black fur (given) = 16
Total = 2 + 16 = 18
Next, we use the proportion of squirrels that have brown-black fur:
Proportion of brown-black = ( \frac{16}{34} = 0.47 ) (approximately)
Using this value in the Hardy-Weinberg equation, we can estimate the total number of squirrels with brown-black fur.
Step 2
Use all of the information to calculate the actual frequency of the C<sup>b</sup> allele.
Answer
Given that there are 34 squirrels and 16 have brown-black fur, we can calculate:
The frequency of the C<sup>b</sup> allele is calculated by determining the number of individuals homozygous recessive (black fur) and heterozygous:
Let ( p ) be the frequency of the C<sup>c</sup> allele and ( q ) that of C<sup>b</sup> allele:
From observed data, ( q^2 = \frac{2}{34} \rightarrow q = \sqrt{\frac{2}{34}} \approx 0.24 )
Thus, frequency of C<sup>b</sup> (rounded to two decimal places) is: ( q \approx 0.24 )
Step 3
Use this information to deduce which one of the following conclusions is most likely true.
Answer
The correct answer is B. The mutation that caused black fur happened in a common ancestor of S. carolinensis and other closely related species. This conclusion is based on the observation that the same mutation appears in both groups of organisms.
Step 4
Calculate the percentage reduction in size of the protein coded for by the C<sup>b</sup> allele compared with the protein coded for by the C<sup>c</sup> allele.
Answer
To calculate the percentage reduction in protein size:
- Determine the size of the protein coded by the C<sup>c</sup> allele, which we assume to be longer than 306 amino acids. Let’s say it is 310 amino acids (as this is an example).
- Calculate the reduction: ( Reduction = (310 - 306) = 4 )
- Calculate the percentage reduction:
( Percentage\ reduction = \left( \frac{4}{310} \right) \times 100 \approx 1.29% ) (to three significant figures, it would be 1.29).
Step 5
Use Figure 1 to discuss the relationship between gene C<sup>b</sup> and fur color.
Answer
Figure 1 illustrates the biochemical pathway related to fur color in S. carolinensis. This suggests that the C<sup>b</sup> allele leads to a receptor protein that is not activated in the presence of the hormone αMSH. Therefore, in the presence of C<sup>b</sup>, less dark pigment is produced, resulting in brown-black fur rather than dark fur. Thus, the C<sup>b</sup> allele influences the color by altering the receptor's activation, leading to a lighter fur phenotype.