Question

Assertion: The reciprocal cross considering eye color in Drosophila did not follow the classical genetics ratio

Reason: Gene for eye color is sex-linked

• A. Both assertion and the reason are true and the reason is a correct explanation of the assertion
• B. Both the assertion and reason are true but the reason is not the correct explanation of the assertion
• C. Assertion is true but the reason is false
• D. Both the assertion and reason are false

Answer 1

The correct option is A Both assertion and the reason are true and the reason is a correct explanation of the assertion

T.H. Morgan’s work on Drosophila brought to light the role of chromosomes in heredity. For eye colour, the reciprocal cross results were not identical, which suggests that the gene for the eye colour is located on the X chromosome.
A cross between a red-eyed male $\left(X^{+}Y\right)$ and a red-eyed female $\left(X^{+}{X}^w\right)$ results in a 3:1 ratio of red to white where all females are red-eyed.
A cross between a white-eyed male $\left(X^{w}Y\right)$ and a red-eyed female $\left(X^{+}{X}^w\right)$ results in a 1:1:1:1 ratio of red-eyed females to white-eyed females to red-eyed males to white-eyed males. Thus both assertion and the reason are true and the reason is a correct explanation of the assertion.