Question

Assertion: Starch synthesis in pea seeds is controlled by one gene.
Reason: Occasionally, a single gene product may produce more than one affect.
A. Both assertion and reason are correct and the reason is the correct explanation of assertion.
B. Both assertion and reason are correct by assertion is not the correct explanation of assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

Hint: The problem is based on pleiotropy. It is a form of inheritance where one single gene expresses two different phenotypic traits in an organism.

Complete answer:
Pleiotropy occurs when one gene regulates the expression of unrelated phenotypic traits. Such a gene is called a pleiotropic gene. Different target cells have the same signaling cascade.
The gene controlling starch synthesis in pea exhibits pleiotropy. The gene regulates the starch synthesis and the shape of the seed. It has two alleles, B and b. Starch is synthesized by BB homozygotes and large starch granules are produced. In contrast, bb have lower starch synthesizing efficiency and produce smaller sized starch grains. Bb heterozygote shows its effect in the production of the intermediate size of starch grains and the shape of the seed. Bb shows incomplete dominance with respect to starch synthesis but when considered for seed shape, B is dominant over b.
Hence both assertion and reason are correct but the reason is not the correct explanation of assertion.
The correct answer is option B.

Note: Sickle cell anemia is an example of pleiotropy in humans. Mendel also found that the gene expressing the flower color was also associated with seed coat and axil pigmentation.