Question

Consider that recombination occurs in 2 strand stage of meiosis. If a Drosophila is heterozygous for the bar locus what will be the result of recombination?

(a) The recombination will make them homozygous

(b) It will produce ultra bar phenotype

(c) It will be heterozygous

(d) No exchange

I had been asked this question in my homework.

This interesting question is from Linkage and Crossing Over in chapter Genetic Recombination of Cytogenetics

Answer 1

The correct answer is (c) It will be heterozygous

Easiest explanation: The exchange in two strand stage will lead to the initial strand having 2 copies of Bar becomes normal and the normal chromosome has two copies. But the resultant will still be heterozygous. Only exchange in 4 strand stage will give ultra-bar.