Question

Suppose that the "fabulous" phenotype is controlled by two genes, A and B, as shown in the diagram below. Allele A produces enough enzyme 1 to convert "plain" to "smashing." Allele a produces no enzyme 1. Allele B produces enough enzyme 2 to convert "smashing" to "fabulous." Allele b produces no enzyme 2. The A and B genes are both autosomal and assort independently. A true-breeding "fabulous" father and a true-breeding "plain" mother (aa bb) mate. What will be the expected ratio of the F_2 offspring from the F_1 generation? 9 "fabulous" 7 "plain" 13 "fabulous" 3 "plain" 9 "fabulous": 3 "smashing": 4 "plain" 12 "plain" 3 "fabulous" 1 "smashing" 15 "fabulous": 1 "smashing"

Answer 1

The expected ratio of the F_2 generation from F_1 generation will be

9 "fabulous": 3 "smashing": 4 "plain"

Step-by-step explanation:

The expression of the phenotype will follow Mendel's Dihybrid cross.

plain→smashing

(only when allele A is present, which produces Enzyme 1)

smashing→fabulous

(only when allele B is present, which produces Enzyme 2)

Keeping the above statements in mind, in F_2 generation, only the genotypes having both A and B alleles will express phenotype "fabulous",as both Enzyme 1 and Enzyme 2 are required for that. The genotype having at-least one A allele and no B allele will produce the phenotype "smashing", as Enzyme 1,produced by allele A, will convert "plain" into "smashing". Hence, the dihybrid cross will as in the attachment.