Revision summary
Polymorphism is two or more common alleles at a locus. Balanced types include sickle cell and malaria. ABO, Rh, and HLA are serological polymorphisms. SNPs and STRs are DNA types used in medicine and forensics. Most human genetic variation is polymorphic within populations.
Model answer
Copper italics in this answer — like this — are the key facts. Each one is unpacked in the Facts & figures rail.
Introduction
Genetic polymorphism is the stable presence of two or more alleles at a locus, each at a frequency too high to be only recurrent mutation. A common teaching cut-off is 1 percent.
Body
Definition
- Ford used polymorphism for discrete forms in a population. In humans it now covers blood groups, enzymes, and DNA sites.
- It is not a rare disease allele. It is a normal variation that population genetics can count.
Types and examples
- Balanced polymorphism: heterozygote advantage. Sickle haemoglobin in malaria belts, shown by Allison, and thalassaemia in parts of India and the Mediterranean.
- Transient polymorphism: a rising advantageous allele not yet fixed, or a falling one.
- Chromosomal polymorphism: inversions in Drosophila were the classic; humans show copy-number and inversion variants too.
- Protein / serological: ABO, Rh, HLA, G6PD.
- DNA polymorphism: SNPs, STRs used in forensics, Alu insertions.
- Restricted vs widespread: PTC tasting, lactase persistence as gene–culture polymorphism.
Meaning
- Polymorphism feeds Harris enzyme work and Lewontin’s point that most variation is within groups.
Flow diagram
flowchart TD GP[Genetic polymorphism] --> BAL[Balanced sickle] GP --> DNA[SNP STR] GP --> SER[ABO Rh HLA]
Conclusion
Genetic polymorphism is common allelic variation. Types run from balanced sickle-cell systems to SNPs and STRs, and they are the raw material of human diversity.
Quick related
Students also ask
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Is a 0.1 percent disease allele a polymorphism?
Usually no. The teaching definition wants appreciable frequency in the population.
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Is polymorphism the same as polytypism?
Polytypism is between-population difference. Polymorphism is variation within a breeding population.
Same topic · past papers
UPSC has asked this before
These previous-year questions sit on the same topic. Open one to practise the earlier ask.
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2026 · Q1(d) · Anthropology GS 1 · 10 marks
Genetic polymorphism and natural selection. -
2022 · Q5(a) · Anthropology GS 1 · 10 marks
Balanced and transient genetic polymorphism -
2026 · Q3(a) · Anthropology GS 1 · 20 marks
How do the concepts of power, authority, legitimacy and social control change with changing political organization? Discuss in detail giving suitable examples -
2026 · Q3(c) · Anthropology GS 1 · 15 marks
Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples -
2026 · Q6(a) · Anthropology GS 1 · 20 marks
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More from this topic
Q1(d) · UPSC Mains 2026 · Anthropology GS 1 · 10 marks · Solution
Genetic polymorphism and natural selection.
Concept of genetic polymorphism and selection, Mendelian population, Hardy-Weinberg law
Genetic polymorphism is the presence of multiple alleles in a population at frequencies too high for mutation alone.
Q7(b) · UPSC Mains 2023 · Anthropology GS 1 · 15 marks · Solution
What assumptions must be met for a population to be in genetic equilibrium. Explain the importance of genetic equilibrium.
Concept of genetic polymorphism and selection, Mendelian population, Hardy-Weinberg law
Hardy and Weinberg showed that p², 2pq, and q² persist under stated assumptions. Assumptions are large size, random mating, and no mutation, migration, or selection. Equilibrium is the null against which evolution is inferred. Forensics and counselling use it to get genotype frequencies. Sickle-cell selection and isolate inbreeding are standard anthropological departures. Real populations only approximate the model.
Q5(a) · UPSC Mains 2022 · Anthropology GS 1 · 10 marks · Solution
Balanced and transient genetic polymorphism
Concept of genetic polymorphism and selection, Mendelian population, Hardy-Weinberg law
Polymorphism is lasting allelic diversity at one locus. Balanced polymorphism keeps alleles, classically by heterozygote advantage. Sickle-cell and malaria is the human type case. Transient polymorphism is a passing stage while one allele replaces another. Lactase persistence is a human illustration of a sweep still in motion.