Thomas Hunt Morgan crossed a white-eyed male with red-eyed females in a parental generation and then brother-sister mated the F₁ offspring and examined their F₂ progeny. Morgan observed all of the following in his crosses. Which of these observations is NOT expected of simple Mendelian inheritance of a recessive allele?

Question

Quizplus · Accepted Answer

White eyes appeared only in males in the F₂ generation is not expected of simple Mendelian inheritance of a recessive allele. In simple Mendelian inheritance, the recessive allele is only expressed in the homozygous recessive genotype. In this case, the white-eyed allele is recessive to the red-eyed allele. Therefore, the white-eyed phenotype would only be expected to appear in the F₂ generation if both parents were homozygous recessive for the white-eyed allele. However, in Morgan's cross, the F₁ generation flies all had red eyes, which indicates that the white-eyed male parent was heterozygous for the white-eyed allele. Therefore, the white-eyed phenotype would be expected to appear in both males and females in the F₂ generation.

Thomas Hunt Morgan Crossed a White-Eyed Male with Red-Eyed Females