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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. Show your working.
Answer
To use the Hardy-Weinberg principle, we can start by calculating the frequency of the homozygous recessive phenotype (black fur). Given 2 out of 34 squirrels had black fur, we can calculate the frequency as follows:
Let:
- Total population (N) = 34
- Number with black fur = 2
The frequency of individuals with black fur (q²) is:
Thus, the frequency of the allele (q) is:
Since we know the total population (N) and the number with brown-black fur is given as 16, that means:
Square the q to find the frequency of the brown-black individuals:
Thus, the number of brown-black squirrels can be estimated as:
- Total individuals = N * proportion of brown-black fur = 34 * (1 - 0.0588) ≈ 34 * 0.941 = 31.99. The estimated number of brown-black squirrels is therefore approximately 32.
Step 2
Use all of the information to calculate the allele frequency of the C^b allele. Do not use the Hardy-Weinberg equation in your calculation.
Answer
The total population of squirrels is 34, and we know the number of brown-black fur squirrels is 16.
To find the frequency of the C^b allele, we will work out the genotypes involved:
- Let the population with brown-black phenotype be represented by 16. The remaining total with grey fur would be (34 - 16 - 2) = 16. Thus, Frequency of C^b allele (C^b) can be calculated as: Rounding to two decimal places gives 0.47.
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 supported by the observation that both North American and UK species of S. carolinensis show identical phenotypic variations.
Step 4
Calculate the percentage reduction in size of the protein coded for by the C^b allele compared with the protein coded for by the C allele.
Answer
The protein coded for by the C allele is presumed to be 306 amino acids long. Since the C^b allele has a deletion mutation resulting in a smaller protein (size not mentioned but could be assumed here), if we equate C^b as x amino acids long:
To calculate the percentage reduction: To get the rate of reduction, substituting x for the length calculated gives the required answer to 2 decimal figures.
Step 5
Use Figure 1 and this information to suggest why S. carolinensis with the genotype C^c have black fur rather than grey fur.
Answer
The presence of the C^c allele leads to the production of a receptor protein for a hormone called αMSH. If the αMSH binds to this receptor, it triggers the activation of the receptor protein, resulting in the production of dark pigments. Thus, S. carolinensis with the C^c genotype produces more dark pigments, leading to a black fur phenotype.