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1. What is meant by the term phenotype? 2 - AQA - A-Level Biology - Question 7 - 2017 - Paper 1
Question 7
1. What is meant by the term phenotype? 2. The inheritance of fruit colour in summer squash plants is controlled by two genes, A and B. Each gene has two alleles. F... show full transcript
Worked Solution & Example Answer:1. What is meant by the term phenotype? 2 - AQA - A-Level Biology - Question 7 - 2017 - Paper 1
Step 1
Step 2
Step 3
What fruit colour would you expect the following genotypes to have?
Answer
For the genotype AABb, you would expect the fruit colour to be white, as the presence of the dominant AA will influence the outcome. For the genotype aaBB, the expected fruit colour would be yellow, since both recessive alleles at the A locus will allow the B locus to exhibit its dominant trait.
Step 4
Complete the genetic diagram to show all the possible genotypes and the ratio of phenotypes expected in the offspring of this cross.
Answer
Genotypes of offspring: AaBb, Aabb, aaBb, aabb
Phenotypes of offspring: White (A_B_), Yellow (A_bb), Green (aaB_), and White (aabb).
Ratio of phenotypes: 9:3:3:1.
Step 5
Use the Hardy–Weinberg equation to calculate the percentage of plants that were heterozygous for gene B.
Answer
Let p represent the frequency of the dominant allele and q represent the frequency of the recessive allele. Since 36% of the plants are yellow (homozygous recessive), we have:
Hence, p = 1 - q = 0.4. The frequency of heterozygous plants can be calculated using:
Therefore, 48% of the plants are expected to be heterozygous for gene B.