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The graph below shows changes in allele frequencies at a single locus with two alleles B and b in two very large populations - VCE - SSCE Biology - Question 7 - 2005 - Paper 1
Question 7
The graph below shows changes in allele frequencies at a single locus with two alleles B and b in two very large populations. The phenotype resulting from allele B i... show full transcript
Worked Solution & Example Answer:The graph below shows changes in allele frequencies at a single locus with two alleles B and b in two very large populations - VCE - SSCE Biology - Question 7 - 2005 - Paper 1
Step 1
In which population, X or Y, is selection occurring against the homozygous recessive phenotype? Explain your response.
Answer
Selection against the homozygous recessive phenotype is occurring in population X. This is evidenced by the decreasing frequency of the allele b over time. As the frequency of allele b decreases, it indicates that individuals with the homozygous recessive phenotype are being selected against.
Step 2
Describe what has occurred in population Y by the 60th generation.
Answer
By the 60th generation, the frequency of allele b in population Y has become fixed at 1, indicating that allele b has completely replaced allele B. This suggests that selection has favored allele b, resulting in its complete dominance within the population.
Step 3
Given the results in population Y, why has a similar pattern of events not occurred in population X?
Answer
A similar pattern has not occurred in population X likely due to continuous selection pressures against the homozygous recessive phenotype, which prevents allele b from reaching fixation. The environment may favor the dominant phenotype associated with allele B, maintaining genetic diversity within population X.