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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

Immunogenetics — 2015 Paper I

Question · 2015 · Paper I · 15 Marks

What do you understand by Immunogenetics ? Explain with suitable examples.

Model Answer

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Approach

  • Demand of Question: Explain immunogenetics as the study of genetic control of immune responses and illustrate its relevance through human antigen systems and disease associations.
  • Structuring the Response: Define the field, discuss HLA/MHC and immunoglobulin genetics, then illustrate applications in transplantation, disease susceptibility and blood-group incompatibility.
  • Key Dimensions to Cover: HLA, MHC, immune-response genes, antigen presentation, immunoglobulin diversity, transplantation, HLA-B27, autoimmune disease and Rh incompatibility.

Model Answer

Introduction: Immunogenetics is the branch of genetics concerned with the genetic basis of immune-system development, variation and response. It studies how inherited differences influence antigen recognition, antibody production, transplantation compatibility and susceptibility or resistance to disease.

Thus:

Genes → Immune molecules → Immune response → Health/Disease

Major areas of immunogenetics

  1. Major Histocompatibility Complex

The most important human immunogenetic system is the Human Leukocyte Antigen (HLA) complex, located on the short arm of chromosome 6.

It represents the human Major Histocompatibility Complex (MHC).

HLA molecules play a central role in presenting antigenic peptides to T lymphocytes.

Major classes

MHC Class I:

  • HLA-A;
  • HLA-B;
  • HLA-C.

They occur on most nucleated cells and present endogenous peptides mainly to CD8+ T cells.

MHC Class II:

  • HLA-DP;
  • HLA-DQ;
  • HLA-DR.

They occur principally on professional antigen-presenting cells and present exogenous peptides mainly to CD4+ T cells.

Thus:

Antigen processing → HLA presentation → T-cell recognition → Immune response

  1. Extreme HLA polymorphism

HLA loci contain extraordinarily large numbers of alleles.

This diversity is adaptive because different HLA molecules can present different pathogen-derived peptides.

At the population level:

High HLA diversity → Wider repertoire of antigen recognition

Natural selection, including forms of balancing selection, has contributed to maintaining HLA variation.

Anthropological significance

Differences in HLA allele frequencies have been studied for:

  • population relationships;
  • migration history;
  • genetic diversity.

However, interpretation should use multiple genetic markers rather than a single HLA allele.

  1. HLA and transplantation

HLA compatibility strongly influences the success of many organ and especially haematopoietic stem-cell transplants.

Greater donor-recipient matching reduces the probability of serious immune incompatibility.

Thus:

HLA typing → Donor matching → Improved transplant compatibility

This represents one of the most important medical applications of immunogenetics.

  1. HLA and disease susceptibility

Certain HLA alleles are statistically associated with particular diseases.

HLA-B27

HLA-B27 is strongly associated with ankylosing spondylitis.

However:

HLA-B27 ≠ Disease certainty

Many individuals with HLA-B27 never develop the disorder. It therefore represents genetic susceptibility rather than simple Mendelian causation.

HLA-DQ2/DQ8

These alleles are strongly associated with coeliac disease.

Again, genes interact with environmental exposure—in this case dietary gluten.

Thus:

Genetic susceptibility + Environmental exposure → Disease risk

  1. Immunoglobulin genetics

Antibodies or immunoglobulins possess extraordinary diversity.

Their genes are organized in segments that undergo somatic rearrangement during lymphocyte development.

The major segments include:

V + D + J

for heavy chains and:

V + J

for light chains.

Through:

  • V(D)J recombination;
  • junctional diversity;
  • somatic hypermutation;
  • class-switch recombination,

the immune system generates an enormous antibody repertoire from a limited number of inherited gene segments.

This illustrates an important feature of immunogenetics:

Inherited gene architecture + Somatic rearrangement → Antibody diversity

  1. Blood-group immunogenetics

Blood-group antigens are also genetically determined.

ABO system

Alleles at the ABO locus determine the presence of A and B carbohydrate antigens on red blood cells.

The system has importance in:

  • blood transfusion;
  • population genetics;
  • clinical immunology.

Incompatible transfusion can produce an antigen-antibody reaction leading to haemolysis.

  1. Rh system

The Rh system, especially the D antigen, provides another classic immunogenetic example.

An Rh-negative mother carrying an Rh-positive fetus can become sensitized to the D antigen.

In a subsequent incompatible pregnancy:

Maternal anti-D IgG → Placenta → Fetal RBC destruction

This can cause haemolytic disease of the fetus and newborn.

Preventive administration of anti-D immunoglobulin greatly reduces sensitization.

  1. Genetic defects of immunity

Inherited mutations can impair immune function.

Examples include:

  • certain forms of Severe Combined Immunodeficiency (SCID);
  • complement deficiencies;
  • inherited defects affecting phagocyte function.

Such conditions demonstrate directly how genes regulate immune-system components.

  1. Autoimmune diseases

Genetic variation can alter susceptibility to inappropriate immune responses against the body's own tissues.

Examples of disorders with important genetic contributions include:

  • type 1 diabetes mellitus;
  • coeliac disease;
  • ankylosing spondylitis;
  • rheumatoid arthritis.

Most are multifactorial rather than determined by a single gene.

Broader applications

Immunogenetics contributes to:

  1. transplantation medicine;
  2. diagnosis of immune deficiencies;
  3. autoimmune-disease research;
  4. vaccine-response research;
  5. population genetics;
  6. personalized medicine.

Anthropological significance

Immunogenetic markers demonstrate that human biological variation reflects:

Mutation + Selection + Gene flow + Genetic drift + Population history

Pathogens themselves have exerted powerful selective pressures on human populations.

Therefore immunity is a particularly important domain of human biological adaptation.

Conclusion

Immunogenetics examines how hereditary variation shapes antigen recognition, antibody production, immune compatibility and disease susceptibility. HLA polymorphism, HLA-B27-associated susceptibility, ABO/Rh systems and immunoglobulin gene rearrangement demonstrate the close relationship between genetics, immunity, environment and human evolution.

2026 Canalization and catch-up growth. 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.

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UPSC Anthropology Optional 2015 — Paper I

28 questions

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10 Marks150 words
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10 Marks150 words
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10 Marks150 words
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10 Marks150 words
Syllabus: Paper I > 6. Anthropological Theories > Historical Particularism (Boas)
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10 Marks150 words
Syllabus: Paper I > 3. Economic Organization > Modes of subsistence > Horticulture
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10 Marks150 words
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10 Marks150 words
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10 Marks150 words
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10 Marks150 words
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10 Marks150 words
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