All the offspring of a cross between a black-eyed Mendelian and an orange-eyed Mendelian have black eyes. What is the expected phenotypic ratio of a cross between two orange-eyed Mendelian?
A)3 black-eyed:1 orange-eyed
B)0 black-eyed:1 orange-eyed
C)1 black-eyed:3 orange-eyed
D)1 black-eyed:0 orange-eyed

Question

Quizplus · Accepted Answer

All offspring of a cross between a black-eyed and an orange-eyed Mendelian are black-eyed, which means the black-eyed trait is dominant. Therefore, the black-eyed parent must have been a heterozygote (Bb) and the orange-eyed parent must have been homozygous recessive (bb).
When two orange-eyed Mendelians are crossed, both parents must be homozygous recessive (bb). The only possible outcome is that all offspring will have orange eyes (bb genotype). Therefore, the expected phenotypic ratio is 0 black-eyed: 1 orange-eyed.

All the Offspring of a Cross Between a Black-Eyed Mendelian