Question

In Morgan’s dihybrid cross considering body colour and eye colour in Drosophila, 98.7% of the progenies had parental combination flies and 1.3% of the progenies were of non-parental types. This means that the genes controlling body colour and eye colour are

• A. located very near on the same chromosome
• B. present on different chromosomes
• C. located on autosomes
• D. located very far on the same chromosome

Answer 1

The correct option is A located very near on the same chromosome

Linkage is the phenomenon of physical association of the genes on a chromosome which have the tendency to stay close together and get inherited together as a unit without separation. The chances of tightly linked genes (those that are located very close to each other) getting separated by crossing over is very less. Hence, the progenies with parental phenotype will be quite high as compared to the progenies with recombinant phenotypes.
As given in the question, the flies with parental combination (98.7%) are more than that of recombinant phenotypes (1.3%), hence, it can be inferred that the genes controlling body colour and eye colour have a tendency to get transmitted together from the parents to the offspring. This is possible only when the genes are present on the same chromosomes, positioned very close to each other. In other words, the genes are linked.
In his experiments Morgan was able to infer that the gene for eye colour and body colour were located on the sex chromosomes and not the autosomes.