Question

When Morgan chose body colour and eye colour to be the characters for dihybrid crosses in Drosophila, he obtained a greater percentage of parental traits in the progeny. Which of the following inferences can be drawn from the above observation?

• A. The progeny were a result of asexual reproduction, hence were identical to the parents.
• B. The genes for these characters were inherited as a single unit.
• C. The genes for these characters were located far apart on the same chromosome.
• D. The genes were located on autosomes.

Answer 1

The correct option is B The genes for these characters were inherited as a single unit.

Morgan chose body colour (brown is dominant over yellow) and eye colour (red is dominant over white) for dihybrid cross in Drosophila.

The appearance of greater number of parental combinations in the progeny proves that the genes for these characters were inherited as a single unit. This is because of the close physical association of the genes, referred to as ‘linkage’. It means the genes were located very close to each other on the same chromosome.

The progeny were a result of sexual reproduction, not asexual reproduction. Under natural conditions, Drosophila doesn’t reproduce asexually.

Whether the genes are located on autosomes or sex chromosomes, cannot be concluded from this observation. Morgan had earlier conducted monohybrid experiment taking eye colour of Drosophila into consideration and had concluded that the gene for eye colour is located on the X chromosome.