Q.9 Example of multiple allelism is
(1) ABO blood grouping
(2) Drosophila eye colour
(3) MN blood grouping
(4) Pea plant height
Multiple Allelism Explained: MCQ Answer & Genetics Breakdown
Multiple allelism occurs when a single gene locus has three or more alleles in a population, though individuals inherit only two (diploid). These alleles create multiple phenotypes/combinations. In the MCQ: “Example of multiple allelism is,” the correct answer is (1) ABO blood grouping.
ABO system has three alleles (I^A, I^B, i) producing four phenotypes (A, B, AB, O) via codominance/incomplete dominance. Classic textbook example of multiple alleles.
Correct Answer: Option (1) – ABO Blood Grouping
ABO Genetics:
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Alleles: I^A (A antigen), I^B (B antigen), i (no antigen)
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Three alleles, multiple interactions:
Genotype Phenotype I^A I^A, I^A i A I^B I^B, I^B i B I^A I^B AB (codominant) ii O
Evidence: Discovered by Karl Landsteiner (Nobel 1930). Population genetics shows all three alleles coexist.
Why Not the Other Options? Detailed Analysis
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Option (2) Drosophila Eye Colour: Incorrect. Two alleles primarily (wild red vs. white recessive). Multiple eye colors exist but from different genes (vermilion, scarlet, brown), not multiple alleles at one locus.
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Option (3) MN Blood Grouping: Incorrect. Only two alleles (M and N) producing three genotypes (MM, MN, NN). Not multiple allelism (requires ≥3 alleles).
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Option (4) Pea Plant Height: Incorrect. Mendel’s classic two alleles (T = tall dominant, t = dwarf recessive). Single gene, diallelic inheritance.
Comparison Table: Multiple Alleles vs. Others
| Option | # Alleles | Phenotypes | Multiple Allelism? | Gene Interactions |
|---|---|---|---|---|
| (1) ABO | 3 (I^A, I^B, i) | 4 (A,B,AB,O) | ✅ Yes | Codominance |
| (2) Drosophila eye | 2 main | Multiple (diff genes) | ❌ No | Polygenic |
| (3) MN blood | 2 (M,N) | 3 | ❌ No | Codominance |
| (4) Pea height | 2 (T,t) | 2 | ❌ No | Complete dominance |
Key Exam Concepts & Applications
Multiple Allelism Examples:
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Human: ABO, Rh factor (C, D, E alleles)
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Rabbit coat color (C, c^ch, c^h, c)
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Mouse coat color (9 alleles!)
Distinguish from:
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Incomplete dominance (2 alleles)
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Polygenic inheritance (multiple genes)
Essential for NEET Genetics, CSIR NET, where ABO exemplifies multiple alleles vs. Mendelian diallelic traits.
Pro Tip: “ABO = 3+ alleles → Multiple allelism. MN = 2 alleles → Not multiple.”
