Compare in any three ways the chromosomal theory of inheritance as proposed by Sutton and Bovery with that of experimental results on pea plant presented by Mendel.

OR

(a) Explain linkage and recombination as put forth by T.H. Morgan based on his observations with Drosophila melanogaster crossing experiment.
(b) Write the basis on which Alfred Sturtevant explained gene mapping.

OR

a) Morgan crossed yellow bodied and white-eyed females with wild-type brown bodied and red -eyed male.

F₁ females were wild type and F₁ males has both mutant traits.

F₁ progenies were intercrossed. F₂ progenies showed that the genes did not show much segregation and majority of the phenotype (98.7%) shown is of parent progeny.

This phenomenon is called linkage. The closely linked genes show very less recombination. Morgan concluded that two genes located close to each other are unlikely to segregate and hence tightly linked.

b) Alfred Sturtevant used the distance between the genes as recombination frequency between gene pairs on same chromosomes. This is how he ‘mapped’ the position on the chromosome. He used the simple logic that distance between genes is directly proportional to the percentage recombinants.