Question

Thomas Hunt Morgan carried out several dihybrid crosses in Drosophila melanogaster to study genes that were sex linked.
(a) Give four major reasons for using the tiny fruit flies by Morgan for his experiments.
(b) How did Morgan and his group explain the physical association of the two genes on a chromosome to the frequency of recombination between gene pairs on the same chromosome?

Hint:

Linkage reduces recombination frequency; closely linked genes are often inherited together.

Answer 1

(a) Step 1: Reasons for using Drosophila melanogaster:

• Easy to rear in laboratory.
• Short life cycle of about 2 weeks.
• Produces large number of progeny.
• Clear and distinguishable sexual dimorphism and genetic traits.

(b) Step 2: Morgan and his group observed that genes located on the same chromosome tend to be inherited together.
Step 3: The frequency of recombination between two genes is directly proportional to the physical distance between them on a chromosome. 
Step 4: This led to the concept of gene linkage and genetic mapping based on recombination frequency.