Question

Assertion: The red eye color in Drosophila is dominant over white eye

Reason: The gene for white eye is present on the X chromosome and both the gene and trait is said to be X-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 B Both the assertion and reason are true but the reason is not the correct explanation of the assertion

In Drosophila XY system of sex determination is followed where males are heterogametic (XY) and females are homogametic (XX). Thus males inherited their only X chromosome from their mother (maternal inheritance) while in females one X chromosome is from the father (paternal inheritance). So a cross between white eye female (undefined) and red-eye male (undefined) yields all white-eye males and all red-eyed females, this result shows that the eye colour gene is present on the X chromosome and thus both the gene and trait is said to be X-linked.
To prove that the red eye colour in Drosophila is dominant over white eye we have to take a cross between a heterozygous red eyed female (undefined) and a red eyed male (undefined) .
The offspring exhibits a 3:1 ratio of red to white, which indicates that the white eye is a recessive character. Thus both the assertion and reason are true but the reason is not the correct explanation of the assertion.