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Mutation is one cause of genetic variation in organisms - AQA - A-Level Biology - Question 6 - 2020 - Paper 2
Question 6
Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation. 1 2 In a species of flowering plant, the T allele for tallne... show full transcript
Worked Solution & Example Answer:Mutation is one cause of genetic variation in organisms - AQA - A-Level Biology - Question 6 - 2020 - Paper 2
Step 1
Step 2
Step 3
Complete the genetic diagram to show all the possible genotypes and the ratio of phenotypes expected in the offspring of this cross.
Answer
Phenotypes of parents: Dwarf, pink-flowered × Tall, white-flowered.
Genotypes of parents: ttc<sup>R</sup>w and TtC<sup>w</sup>.
Genotypes of offspring: ttc<sup>R</sup>w, TtC<sup>w</sup>.
Phenotypes of offspring: Dwarf, pink-flowered and Tall, white-flowered.
Ratio of phenotypes: 1 : 1.
Step 4
Calculate the percentage of pink-flowered plants in this population.
Answer
Let p be the frequency of the dominant allele (red), and q be the frequency of the recessive allele (white).
The frequency of red-flowered plants is given as 9%, so p² = 0.09. Thus, p = √0.09 = 0.3.
Since p + q = 1, we have q = 1 - 0.3 = 0.7.
The percentage of pink-flowered plants is given by 2pq:
2pq = 2 × 0.3 × 0.7 = 0.42, or 42%.