Question

Frequency of crossing over increases with

• A. decreasing availability of synaptonemal complexes
• B. decrease in distance between the two genes
• C. increase in strength of linkage
• D. increase in distance between the two genes

Answer 1

The correct option is D increase in distance between the two genes

In crossing over, homologous chromosomes pair and exchange their genetic materials through their non-sister chromatids' segments. This gives rise to new combinations of alleles.
On the other hand, if the 2 genes are close together, with very less distance between them, they act as a single unit and hinder the occurrence of crossing over. The closer the genes are, the more hindrance they provide to crossing over. So, we can say that the frequency of crossing over increases with the increase in distance between the 2 genes.
Decreasing the distance between 2 genes will lower the chances of crossing over and increase the strength of linkage i.e. increase the association of the genes to act as a single unit.
Synaptonemal complexes aid in the synapsis. Synapsis is the phenomenon of pairing of homologous chromosomes during prophase I. Synapsis leads to crossing over and recombination. If synaptonemal complexes are unavailable, there would be a decrease in crossing over.