Question

Two Mark Questions :
Linkage and Crossing over of genes are alternatives of each other. Justify with the help of an example.

Answer 1

The linkage is the tendency of certain loci or alleles (genes) to be inherited together while, crossing over is the segregation of genes, e.g. the genes on a chromosome either follow linkage path or cross over, to form the gametes during gametogenesis in human. In Drosophila a yellow bodied white eyed female was crossed with brown bodies red-eyed male, F1 progeny produced and intercrossed the F2 phenotypic ratio of Drosophila deviated significantly from Mendel’s 9:3:3:1, the genes for eye color and body color are closely located on the ‘X’ chromosome showing linkage and therefore inherited together, recombinants were formed due to crossing over but at low percentage.