Question

The genes R, E and D are independently assorting and control production of red pigment as follows (recessive alleles are not functional) precursor -- (R) --> white -- (E) --> yellow -- (D) --> red RREEDD and rreedd individuals are crossed, and their offspring are testcrossed. What proportion of the F2 progeny is expected to be red?

Answer 1

Answer:

1/8

Explanation:

An individual must have all three dominant alleles to be red, in homozygosis or heterozygosis (R_E_D_).

The parental cross was:

RREEDD x rreedd

F1: RrEeDd

The test cross is between the RrEeDd indiviudals and homozygous recessive rreedd.

The genes assort independently, so we can use Mendel's law of segregation to predict separately for each gene the proportion of the offspring that will have the dominant alleles.

Rr x rr

1/2 Rr

1/2 rr

Ee x ee

1/2 Ee

1/2 ee

Dd x dd

1/2 Dd

1/2 dd

Genes are independent, so the probability of having a R_E_D_ offpsring is calculated by multiplying the individual probabilities of having a dominant allele for each gene:

1/2 (Rr) × 1/2 (Ee) × 1/2 (Dd)= 1/8