UPSC Prelims 2002 Q55: Science & Technology – Biotechnology & Genetics
When one gene controls two or more different characters simultaneously, the phenomenon
is called
- (a) Apomixis
- (b) Pleiotropy
- (c) Polyploidy
- (d) Polyteny
Answer: (b) Pleiotropy
Explanation
One gene controlling two or more characters
| Term | Meaning |
|---|---|
| Pleiotropy | One gene affects several characters (e.g. sickle-cell gene, or the gene for white eyes) |
| Apomixis | Seed formation without fertilisation |
| Polyploidy | More than two sets of chromosomes |
| Polyteny | Chromosomes with many chromatids side by side, as in salivary glands |
When a single gene controls two or more different characters at the same time, the phenomenon is called pleiotropy. A well-known example is the gene for sickle-cell anaemia, which affects the shape of the red cell and several other body functions.
Answer: (b) Pleiotropy.
Why each option is right or wrong
- (a) Incorrect. Apomixis is asexual seed formation, not a gene-effect phenomenon.
- (b) CORRECT. Pleiotropy means one gene, many characters.
- (c) Incorrect. Polyploidy is about the number of chromosome sets.
- (d) Incorrect. Polyteny is about giant chromosomes.
Key point
Pleiotropy is the opposite of polygenic inheritance, where many genes control one character.
Remember
Pleiotropy = one gene, many characters.
Common mistakes
- Choosing polyploidy because of the similar prefix 'poly'.
- Mixing pleiotropy with polygenic inheritance.
- Confusing apomixis with genetics of characters.
Exam tip
'Pleio' means many; many effects from one gene.
Sources
- NCERT Class XII Biology — Principles of Inheritance and Variation
- Anthony J. F. Griffiths et al. — Introduction to Genetic Analysis (W. H. Freeman)