Question

Choose the correct alternative among the following with regard to the sample used by Morgan in his monohybrid cross.

• A. Male Drosophila : red eyes :: female Drosophila : brown eyes
• B. Male Drosophila : brown eyes :: female Drosophila : red eyes
• C. Male Drosophila : white eyes :: female Drosophila : red eyes
• D. Male Drosophila : brown eyes :: female Drosophila : brown eyes

Answer 1

The correct option is C Male Drosophila : white eyes :: female Drosophila : red eyes

Morgan performed his experiments with Drosophila melanogaster( also known as fruit fly). In one of his experiments where crossing was done between a red-eyed female (pureline) and a white-eyed male, he observed that all the F1 offsprings were red-eyed.
Finding the possible genotype of the F1 progenies using Punnett square:-
$\begin{array}{cc}\text{Gametes}& X^{w+}\\ X^{w+}& X^{w+}{X}^w\\ & \text{(red eyed female)}\\ X^w& X^{w+}Y\\ & \text{(red eyed female)}\end{array}$
In the F2 generation obtained after crossing between male and female progenies of F1 generation, Morgan observed the following phenotypic ratio:-
Red eyed offsprings : white eyed offsprings = 3 : 1
Interestingly, half of the male offsprings were white eyed and that none of the female flies were with white eyes.
Red eyed male : Red eyed female : White eyed male = 1 : 2 : 1
This reflected the possibility of presence of the gene responsible for eye color on the X chromosome.The F2 male progeny with white eyes inherited the allele responsible for white eye color from the F1 female (heterozygous for red e ye color). F1 inherited the same from the male in the parental generation. This had the same inheritance pattern as that of the X chromosome.