3. The number of alleles possible for a gene is:
a. 2
b. Infinite
c. 4
d. 1
Allele Definition
An allele represents any DNA sequence variant at a specific gene locus. While diploid organisms inherit exactly two alleles per gene (one per homologous chromosome), populations harbor multiple alleles from mutational diversity. Mendel’s peas showed two, but modern genetics recognizes limitless possibilities.
Option Analysis
- a. 2: Incorrect for populations; limits to diploid individual level only, ignoring population-level polymorphism.
- b. Infinite: Correct; mutations generate unlimited alleles (SNPs, indels), as seen in human MHC with thousands .
- c. 4: Incorrect; no biological basis for exactly four; multiple alleles exceed this (e.g., ABO blood has 6+ common).
- d. 1: Incorrect; single allele implies no variation, contradicting genetic diversity essential for evolution .
CSIR NET Implications
Questions test distinction between individual (2 alleles) vs population (many/infinite). Genotype count formula \( G = \frac{a(a+1)}{2} \) shows exponential growth with allele number \( a \) . Aspirants: memorize examples like Drosophila eye color (>100 alleles).
