In Labrador retrievers, B (black) is dominant to b (brown), and E (pigment deposited) is dominant to e (no pigment, yellow coat regardless of B/b). Two heterozygous (BbEe) parents are crossed. What fraction of offspring are expected to be yellow?
- A
(yellow is the most common dihybrid phenotype)
- Bcheck_circle
(epistasis: ee masks B/b → 1/4 of all offspring)
- C
(yellow appears only with B_ee combinations)
- D
(only bbee genotype produces yellow coats)
Explanation
BbEe × BbEe gives 9 B_E_ : 3 bbE_ : 3 B_ee : 1 bbee. ee individuals are yellow regardless of B genotype, so yellow fraction = (3+1)/16 = 4/16 = 1/4.