Question

Which of the following statements is incorrect with respect to Morgan’s dihybrid cross?

• A. Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex-linked.
• B. He observed that the two genes segregate independently of each other and the F2 ratio is 9:3:3:1.
• C. He coined the term linkage to describe the physical association of genes on a chromosome.
• D. Morgan conducted his experiment on Drosophila melanogaster.

Answer 1

The correct option is B He observed that the two genes segregate independently of each other and the F2 ratio is 9:3:3:1.

T.H. Morgan conducted his experiment on Drosophila melanogaster (commonly known as fruit fly). He carried out several dihybrid crosses using Drosophila to study the pattern of inheritance of genes. The crosses were similar to the dihybrid crosses carried out by Mendel in peas, however the outcomes were quite different.
He observed that the two genes did not segregate independently of each other while he crossed brown bodied, red eyed males with yellow bodied, white eyed females. After selfing F1, he observed that these genes were not independently assorted and the F2 phenotypic ratio deviated very significantly from the 9:3:3:1 ratio (expected when the two genes get assorted independently). It was observed that in the F2 generation, there were more offspring of parental type (98.7%) and less percentage of offspring of recombinant type (1.3%).
His observations further provided a concrete evidence of the fact that certain genes were sex-linked. Morgan also coined the term linkage to describe this physical association of genes on a chromosome.