Assertion : When yelow bodied, white eyed Drosophila females were hybridised with brown-bodied, red eyeed males , and `F_(1)` progeny was intercrossed, `F_(2)` ratio deviated from `9:3:3:1`
Reason : When two genes in a dihybrid are on same chromosome, the proportion of parental gene combinations are much higher than the non-parental type

Options

A. If both the assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Answer

A

Explanation

In Drosophila, the genes for body and eye colour are located on X chromosome. When two genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combination are higher than non-parental type. This occurs due to physical association or linkage of the two genes while non-parental gene combinations due to recombination between genes. Thus, linkage and recombination deviates the ratio form Mendelian ratio of a dihybrid cross `(9:3:3:1)`