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Home/Anthropology/Mains PYQ/2024/Paper I/Human Genetics & Human Biology
UPSC MainsAnthropology Optional Paper I 2024 10 Marks Model Answer Available

Heritability and Its Estimation — 2024 Paper I

Question · 2024 · Paper I · 10 Marks

Heritability and its estimation

Model Answer

VAID ICS

Introduction

Heritability is the proportion of variation in a measurable trait within a particular population that is attributable to genetic differences among individuals. The statistical foundation of the concept was laid by R.A. Fisher in 1918 and later developed in quantitative genetics by scholars such as D.S. Falconer.

Heritability does not indicate how much of an individual’s trait is genetic, nor does it imply that the trait is unchangeable.

Components of Phenotypic Variation

Variation in an observable trait may be represented as:

VP = VG + VE + VG×E

where:

  • VP = total phenotypic variance;
  • VG = genetic variance;
  • VE = environmental variance;
  • VG×E = gene–environment interaction.

Genetic variance may be further divided into:

VG = VA + VD + VI

where VA, VD and VI represent additive, dominance and epistatic variance respectively.

Types of Heritability

Broad-sense heritability

H2 = VG / VP

It includes all genetic contributions—additive, dominance and epistatic effects.

Narrow-sense heritability

h2 = VA / VP

It includes only additive genetic variance and is particularly useful for predicting resemblance between relatives and response to natural or artificial selection.

Methods of Estimation

Parent–offspring regression

The value of a trait in offspring is regressed on the average value of both parents.

h2 = regression coefficient of offspring on mid-parent

Greater resemblance between parents and offspring indicates a stronger additive genetic contribution, provided shared environmental effects are controlled.

Twin studies

Monozygotic twins share nearly all their genetic material, whereas dizygotic twins share, on average, about half of their segregating genes. A commonly used estimate is:

h2 = 2(rMZ − rDZ)

where rMZ and rDZ are trait correlations among monozygotic and dizygotic twins.

Adoption studies

Adopted individuals are compared with their biological and adoptive relatives.

  • Resemblance to biological relatives suggests genetic influence.
  • Resemblance to adoptive relatives suggests environmental influence.

Family and pedigree studies

Correlations among full siblings, half-siblings, cousins and other relatives are analysed. Since they share different proportions of genes, their resemblance helps separate genetic and environmental variance.

Analysis of variance

In controlled breeding or family studies, total variation is divided into within-family and between-family components. These variance components are used to estimate genetic contribution.

Response to selection

Realised narrow-sense heritability may be calculated as:

h2 = R / S

where:

  • R = response to selection;
  • S = selection differential.

Genomic methods

Modern studies use genome-wide genetic data to estimate SNP heritability. However, this captures only the variation explained by measured genetic variants and may be lower than heritability estimated from families or twins.

Anthropological Significance

Heritability is useful in studying:

  • stature and body proportions;
  • growth and maturation;
  • craniofacial and dermatoglyphic traits;
  • obesity and blood pressure;
  • disease susceptibility;
  • adaptation and biological variation among populations.

For example, stature may show high heritability in a well-nourished population, but nutritional deprivation can substantially reduce growth and alter population averages.

Limitations and Critical Interpretation

  • Heritability is specific to a population and environment.
  • A high value does not mean that a trait cannot be altered.
  • It explains variation within a population, not differences between populations.
  • Shared family environment may be mistaken for genetic influence.
  • Assortative mating and gene–environment correlation can inflate estimates.
  • Twin studies depend on the assumption that identical and fraternal twins experience comparable environments.
  • Cultural conditions, nutrition, inequality and healthcare may strongly modify trait expression.

Thus, heritability estimates should not be used to justify biological determinism or social inequality.

Conclusion

Heritability is a statistical measure of the contribution of genetic differences to phenotypic variation within a defined population. Its estimation through twin, adoption, family, regression, selection and genomic studies is valuable in biological anthropology. However, it must always be interpreted within the broader interaction of genes, ecology, culture and socioeconomic environment.

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. 2026 What do you understand by fertility and mortality? How are these influenced by biological and socio-ecological factors? 2026 In what manner is our understanding of serogenetics and cytogenetics useful in reproductive biology? What are the major ethical issues involved in reproductive technology?

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UPSC Anthropology Optional 2024 — Paper I

28 questions

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10 Marks150 words
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10 Marks150 words
Syllabus: Paper I > Economic Organization > Reciprocity and Exchange > Kula ring
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10 Marks150 words
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1(e) Hemoglobin in health and disease

10 Marks150 words
Syllabus: Paper I > Human Genetics > Genetic Polymorphism > Haemoglobinopathies; health and disease
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5(c) Heritability and its estimation

10 Marks150 words
Syllabus: Paper I > Human Genetics > Quantitative Genetics > Heritability and its estimation
2024Paper IHuman Genetics & Human BiologyModel answer available

1(d) Lethal and sublethal genes

10 Marks150 words
Syllabus: Paper I > Human Genetics > Mendelian Genetics in Man > Lethal and sublethal genes
2024Paper IHuman Genetics & Human BiologyModel answer available

5(e) Single-gene mutation disorders in man

10 Marks150 words
Syllabus: Paper I > Human Genetics > Mutation and Genetic Disorders > Single-gene disorders
2024Paper IHuman Genetics & Human BiologyModel answer available