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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 in this population had brown-black fur.
Answer
To estimate how many squirrels had brown-black fur, we first identify the alleles present. Since there are three genotypes (C^G C^G for grey, C^G C^B for brown-black, and C^B C^B for black), we can define the frequencies of the alleles.
Let p represent the frequency of C^G and q represent the frequency of C^B. We know from the problem that:
- Total squirrels (N) = 34
- Number of squirrels with black fur = 2
Using the Hardy-Weinberg equation:
We have:
(with p^2 being grey, 2pq being brown-black, and q^2 being black).
Given q^2 = 2/34, we find q = sqrt{(2/34)} = approximately 0.243.
Thus, q ≈ 0.24 and p = 1 - q ≈ 0.76
Now we can find the expected number of brown-black squirrels:
Step 2
Use all of the information to calculate the actual frequency of the C^G allele.
Answer
The actual number of squirrels is given as:
- Brown-black fur = 16
- Total squirrels = 34
To find the actual frequency of the C^G allele:
We use the formula:
.
Each squirrel has 2 alleles, hence total alleles = 34 * 2 = 68.
The number of C^G alleles can be calculated as:
Thus, the frequency of C^G = \frac{number \ of \ C^G}{total \ alleles} = \frac{48}{68} = 0.71 ≈ 0.71.
Step 3
Deductions based on available information.
Answer
Given that S. carolinensis from both regions show the same variation and that an identical black fur mutation exists in related species, the most likely conclusion is:
B. The mutation that caused black fur happened in a common ancestor of S. carolinensis and other closely related species.
Step 4
Calculate the percentage reduction in size of the protein coded for by the C^B allele.
Answer
The length of the protein for the C^G allele is 306 amino acids long.
To calculate the percentage reduction:
Let’s assume that X is the protein length after going through mutation. Without loss of generality, let’s calculate as: