Question

The following seed phenotypes showed up in a generation of plants. Which alleles are recessive? blue round = 75 white round = 28 blue wrinkled = 24 white wrinkled = 8

Answer 1

The answer is white and wrinkled.

It is known that the in dihybrid cross (a cross between two different traits), the phenotypic ratio between the offspring of two heterozygous parents in the F2 generation is 9:3:3:1, where:

- 9 is a number of phenotypes with both dominant traits,

- 3 is a number of phenotypes with the first dominant trait and the second recessive trait,

- 3 is a number of phenotypes with the first recessive trait and the second dominant trait,

- 1 is a number of phenotypes with both recessive traits.

blue round = 75                             (≈ 9 · 8)

white round = 28                           (≈ 3 · 8)

blue wrinkled = 24                         (= 3 · 8)

white wrinkled = 8                         (= 1 · 8)

So, the ratio between the offspring is close to 9:3:3:1 in F2 generation.

Since in the ratio, 1 is the number of phenotypes with both recessive traits, in this example, this phenotype is white wrinkled, so recessive traits are white and wrinkled.