Question

Which genotype classes appear exactly once in the F₂ generation from a dihybrid cross?

Options

• RRYY, RRYy, and RrYY

• RRYY, RRyy, rrYY, and rryy

• RrYy only

• RRYy, Rryy, and rrYy

Answer 1

The four pure-breeding genotypes (homozygous for both genes) appear exactly once in the F₂ generation: RRYY (pure dominant), RRyy (round pure green), rrYY (wrinkled pure yellow), and rryy (pure recessive). These represent the four possible homozygous combinations.