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Home/Anthropology/Mains PYQ/2015/Paper I/Human Genetics & Human Biology
UPSC MainsAnthropology Optional Paper I 2015 15 Marks Model Answer Available

Genetic Polymorphism and Its Types — 2015 Paper I

Question · 2015 · Paper I · 15 Marks

Define genetic polymorphism. Give details of its types with suitable examples.

Model Answer

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Approach

  • Demand of Question: Define genetic polymorphism and explain its principal population-genetic types with appropriate human examples.
  • Structuring the Response: Establish the frequency-based concept, distinguish balanced and transient polymorphism, and illustrate common human polymorphic systems.
  • Key Dimensions to Cover: E.B. Ford, allele frequency, balanced polymorphism, heterozygote advantage, HbS, transient polymorphism, ABO, HLA and DNA polymorphisms.

Model Answer

Introduction: Genetic polymorphism refers to the occurrence, within an interbreeding population, of two or more genetically determined alternative forms at appreciable frequencies such that the rarest form cannot be explained merely by recurrent mutation.

The concept was particularly developed by E.B. Ford.

Conventionally, a locus is termed polymorphic when the frequency of its less common allele is approximately 1% or more, although operational definitions vary.

Thus:

One population + Same locus + Two or more common alleles = Genetic polymorphism

Significance

Genetic polymorphism provides the raw material for:

  • natural selection;
  • adaptation;
  • population differentiation;
  • anthropological reconstruction of population relationships.

Types of genetic polymorphism

  1. Balanced polymorphism

In balanced polymorphism, two or more alleles are maintained in a population for long periods because selection prevents any one allele from completely replacing the others.

Thus:

Selective forces → Maintenance of multiple alleles

Heterozygote advantage

The classic human example is the HbS polymorphism.

Genotypes:

  • HbA/HbA — normal haemoglobin but greater susceptibility to severe falciparum malaria;
  • HbS/HbS — sickle-cell disease;
  • HbA/HbS — partial protection against severe malaria with usually much less severe sickling than HbS homozygotes.

In malaria-endemic environments:

Heterozygote advantage → Persistence of HbA and HbS

This is known as balanced polymorphism due to overdominance.

It is a classic example of interaction between:

Genetics + Environment + Natural selection

Other mechanisms maintaining balanced polymorphism

Polymorphism may also be maintained through:

  • frequency-dependent selection;
  • differing selective pressures in different environments;
  • temporal variation in selection.
  1. Transient polymorphism

A transient polymorphism occurs when one allele is progressively replacing another under directional selection.

During the transition, both forms coexist temporarily.

Thus:

Old allele → Selective replacement → New allele

The population is polymorphic only during the period of evolutionary substitution.

An often-discussed general model is the spread of an advantageous mutation through a population until it approaches fixation.

Unlike balanced polymorphism:

Balanced → Several forms persist

Transient → One form ultimately tends to replace another

Common human polymorphic systems

Genetic polymorphism can also be described according to the biological markers through which variation is detected.

  1. Blood-group polymorphism

The ABO blood-group system is controlled mainly by three alleles:

Iᴬ, Iᴮ and i

It produces the phenotypes:

  • A;
  • B;
  • AB;
  • O.

Allele frequencies vary considerably between human populations, making ABO historically important in population genetics and biological anthropology.

  1. Rh polymorphism

The Rh blood-group system, particularly the D antigen, also shows population variation.

It has medical importance because Rh incompatibility may contribute to haemolytic disease of the fetus and newborn.

  1. Haemoglobin polymorphism

Important variants include:

  • HbA;
  • HbS;
  • HbC;
  • HbE.

Their distributions are influenced partly by population history and selective environments.

The distribution of HbS in malaria-endemic areas is a classic adaptive example.

  1. Enzyme and protein polymorphism

Human populations also show polymorphism in biochemical systems such as:

  • G6PD;
  • haptoglobin;
  • transferrin;
  • various red-cell enzymes.

Some variants, including particular G6PD-deficiency alleles, show relationships with malaria environments.

  1. HLA polymorphism

The Human Leukocyte Antigen (HLA) system is among the most polymorphic regions of the human genome.

Its diversity is important in:

  • immune recognition;
  • transplantation;
  • disease susceptibility.
  1. DNA polymorphism

Modern molecular anthropology uses:

  • SNPs;
  • STRs;
  • VNTRs;
  • insertion-deletion polymorphisms.

STR polymorphisms are especially useful in forensic identification because many loci show high inter-individual variability.

Anthropological importance

Polymorphic markers help anthropologists study:

  • genetic diversity;
  • gene flow;
  • migration;
  • population relationships;
  • adaptation;
  • microevolution.

Thus:

Allele-frequency variation → Population comparison → Evolutionary interpretation

However, single polymorphic systems should not be used to construct rigid racial categories because variation is largely overlapping and distributed clinally among populations.

Conclusion

Genetic polymorphism represents the stable or temporary coexistence of alternative genetic forms within a population. Balanced polymorphism, exemplified by the HbA/HbS system in malarial environments, maintains diversity, whereas transient polymorphism reflects ongoing allele replacement. Blood groups, haemoglobins, HLA and DNA markers demonstrate the enormous polymorphic diversity of human populations and provide important tools for population genetics, evolutionary anthropology and medicine.

2026 Genetic polymorphism and natural selection. 2026 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 Distinguishing features of nuclear and mitochondrial DNA. 2026 How would you find out that a particular disease/disorder is inherited and, if so, in which manner? Elaborate with suitable examples.

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UPSC Anthropology Optional 2015 — Paper I

28 questions

1(a) Archaeological Anthropology.

10 Marks150 words
Syllabus: Paper I > 1.3 Main branches of Anthropology > Archaeological Anthropology
2015Paper IFoundations of AnthropologyModel answer available

5(e) DNA technology in Medicine.

10 Marks150 words
Syllabus: Paper I > 12. Applications of Anthropology > DNA technology in diseases and medicine
2015Paper IApplied & Forensic AnthropologyModel answer available

5(b) Down's Syndrome.

10 Marks150 words
Syllabus: Paper I > 9.4(c) Autosomal aberrations > Down syndrome
2015Paper IHuman Genetics & Human BiologyModel answer available

1(e) Historical Particularism.

10 Marks150 words
Syllabus: Paper I > 6. Anthropological Theories > Historical Particularism (Boas)
2015Paper IAnthropological TheoriesModel answer available

1(d) Horticulture.

10 Marks150 words
Syllabus: Paper I > 3. Economic Organization > Modes of subsistence > Horticulture
2015Paper IEconomic & Political AnthropologyModel answer available

1(c) Incest Taboos.

10 Marks150 words
Syllabus: Paper I > 2.3 Marriage > Rules of marriage > Incest taboo
2015Paper IMarriage & FamilyModel answer available

5(c) Longitudinal method of studying growth.

10 Marks150 words
Syllabus: Paper I > 10. Human growth and development > Methodologies for growth studies > Longitudinal method
2015Paper IHuman Genetics & Human BiologyModel answer available

5(d) Menopause and its impact.

10 Marks150 words
Syllabus: Paper I > 11.1 Relevance of menarche, menopause and other bio-events to fertility
2015Paper IHuman Genetics & Human BiologyModel answer available

5(a) Palaeolithic culture.

10 Marks150 words
Syllabus: Paper I > 1.8(b) Cultural Evolution: broad outlines of prehistoric cultures > Palaeolithic
2015Paper IPrehistoric ArchaeologyModel answer available

1(b) Society and Culture.

10 Marks150 words
Syllabus: Paper I > 2.2 The Nature of Society > Society and culture
2015Paper ICulture & SocietyModel answer available