Question

A cross between two plants that both have yellow flowers produces 80 offspring plants, of which 38 have yellow flowers, 22 have red flowers, and 20 have white flowers. If one assumes that this varia- tion in color is due to inheritance at a single locus, what is the genotype associated with each flower color, and how can you describe the inheritance of flower color?

Answer 1

Always start with the genotypic ratios, because they'll be the same. Since hidden variation is popping out, you can assume that both of the parents are heterozygous. The problems you get will be the F2 ratio of the cross between two homozygous individuals.

1:2:1 is the genotypic ratio for one locus. AA:Aa:aa.

1:2:1 is the phenotypic ratio for incomplete dominance. Incomplete dominance means that the heterozygote expresses differently from either homozygote.

3:1 is the phenotypic ratio for complete dominance.

2:1 is the phenotypic ratio for lethal recessive.