Question

In Drosophila, the gene for white eye mutation is also responsible for depigmentation of body parts. Thus, a gene that controls several phenotypes is called as
a. Oncogene
b. Epistatic gene
c. Hypostatic gene
d. Pleiotropic gene
e. Sex linked gene

Answer 1

Hint: There are several genes found in nature that influence two or more seemingly unrelated phenotypic traits. Due to this reason, mutation in one of these genes may affect several traits simultaneously. Sometimes the effects of such mutations can be good, while on other occasions, they might be fatal to the organism.

Complete answer:
The phenomenon where a single gene influences two or more seemingly unrelated phenotypic traits is called pleiotropy. Such a gene that shows multiple phenotypic expressions is known as a pleiotropic gene.

The term pleiotropy is derived from the Greek word “pleio”, which means “many”, and “tropic”, which means “affecting”.
Examples of pleiotropy:
In Drosophila, the gene that controls white eye mutation is also responsible for depigmentation of body parts.
Amino acid tyrosine is needed for general protein synthesis and is also a precursor for many neurotransmitters (e.g., norepinephrine, dopamine), the pigment melanin, and thyroxine hormone.

Hence, the correct answer is option (D).

Additional information:
During Gregor Mendel’s study of pea plants, he observed that plants with coloured seed coats always had coloured leaf axils and coloured flowers. He also noticed that pea plants with colourless seed coats always had white flowers and no pigmentation on their axils. This means that in Mendel’s pea plants, seed coat colour was always associated with flower and axle colours. Today, we know that these observations were the result of pleiotropy. Here in this case, the seed coat colour gene was not only responsible for seed coat colour, but also for flower and axle pigmentation.

Note: Important things to remember-
• Pleiotropy is often confused with polygenic traits. While in pleiotropy, a single gene affects multiple phenotypic traits, polygeny is the phenomenon in which multiple genes converge to result in a single phenotype.
• The term pleiotropy was formally introduced by the German geneticist Ludwig Plate, in the year 1910.