Revision summary
Genetic polymorphism is the presence of multiple alleles in a population at frequencies too high for mutation alone.
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 refers to the occurrence of two or more discontinuous genetic variants or alleles within a population at frequencies higher than can be accounted for by recurrent mutation alone. Natural selection actively shapes these variations, either by eliminating deleterious traits or by maintaining diversity when multiple alleles confer adaptive advantages in fluctuating environments.
Body
Balanced Polymorphism and Heterozygote Advantage
- Mechanism: Natural selection often maintains polymorphism when the heterozygous genotype possesses a higher fitness than either homozygote.
- Classic Example: The HbS allele for sickle cell anemia persists in malaria-endemic regions because heterozygotes (HbAS) exhibit resistance against Plasmodium falciparum infection.
Environmental Heterogeneity and Selection
- Spatial and Temporal Variation: Fluctuating ecological conditions prevent a single allele from achieving fixation across the entire range of a Mendelian population.
- Niche Diversity: Different morphs or alleles may be favoured in different micro-habitats, preserving overall genetic variability within the gene pool.
Flow diagram
flowchart TD
A[Mendelian Population] --> B[Genetic Polymorphism]
B --> C{Selection Pressure}
C -->|Heterozygote Advantage| D[Balanced Polymorphism Maintained]
C -->|Directional Selection| E[Allele Fixation or Loss]
D --> F[Adaptive Fitness in Heterogeneous Environments]
Conclusion
Genetic polymorphism is thus not merely a transitional phase in evolution, but a strategically maintained reservoir of adaptability. Through mechanisms like balancing selection, populations safeguard their evolutionary potential against unpredictable environmental shifts.
Quick related
Students also ask
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What assumptions must be met for a population to be in genetic equilibrium. Explain the importance of genetic equilibrium.
Next question on this syllabus topic (2023 · Q7(b)). View answer →
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What is genetic polymorphism in physical anthropology?
It refers to the simultaneous occurrence of multiple discrete alleles or phenotypes within a Mendelian population at frequencies too high to be explained by mutation alone.
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How does natural selection maintain genetic polymorphism?
Through balancing selection and heterozygote advantage, where individuals carrying two different alleles have higher reproductive fitness than homozygotes in specific environments.
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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2022 · Q5(a) · Anthropology GS 1 · 10 marks
Balanced and transient genetic polymorphism -
2015 · Q8(b) · Anthropology GS 1 · 15 marks
Define genetic polymorphism. Give details of its types with suitable examples -
2015 · Q7(c) · Anthropology GS 1 · 15 marks
Elucidate the role of Anthropology in selection and monitoring of sports persons
More from this topic
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.
Q8(b) · UPSC Mains 2015 · Anthropology GS 1 · 15 marks · Solution
Define genetic polymorphism. Give details of its types with suitable examples
Concept of genetic polymorphism and selection, Mendelian population, Hardy-Weinberg law
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.