Biology Question on Principles of Inheritance and Variation

Question

Lack of independent assortment of two genes- $A$ and $B$ in fruit fly-Drosophila is due to

Answer 1

Solution

$W$ Bateson (1905) explained the lack of independent assortment in sweet pea and T H Morgan (1910) in Drosophila due to linkage. When genes closely present adhere or link together in a group and transmitted as a single unit, the phenomenon is called linkage. It stops the process of independent assortment. Incomplete linkage is broken down due to the crossing over.
Repulsion is an arrangement in a double heterozygote where a wild type allele of one gene is adjacent to a mutant allele of another gene on the same homologous chromosome. Recombination is the arrangement of genes during meiosis so that a gamete contains a haploid genotype with a new gene combination.
Crossing over is a process occurring in the diplotene stage of prophase $-I$ of meiosis in which, there is exchange of non-sister chromatids, producing genetic recombination.