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Home/Anthropology/Mains PYQ/2023/Paper I/Human Genetics & Human Biology
UPSC MainsAnthropology Optional Paper I 2023 10 Marks Model Answer Available

Polygenic Inheritance — 2023 Paper I

Question · 2023 · Paper I · 10 Marks

Polygenic Inheritance

Model Answer

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Introduction Polygenic inheritance (or Quantitative Inheritance) occurs when a single phenotypic trait is controlled by two or more pairs of genes located on different chromosomes. First synthesized by R.A. Fisher (1918), it explains how Mendelian genetics can produce continuous, graded variation in a population, unlike the discrete traits (e.g., tall vs. dwarf) studied by Mendel.

Key Features of Polygenic Inheritance

  1. Multiple Loci & Additive Effect: The trait is governed by multiple genes. Each dominant allele contributes a small, equal, and additive share to the final phenotype. There is no absolute dominance or recessiveness.
  2. Continuous Variation: Phenotypes do not fall into distinct categories. Instead, they form a gradient or continuous spectrum.
  3. Bell-Shaped Curve (Normal Distribution): In any population, the majority of individuals exhibit an intermediate phenotype (heterozygous), while extreme phenotypes (fully dominant or fully recessive) are rare.

Classic Anthropological Examples

  • Human Skin Color: Studied by C.B. Davenport in Jamaica. He proposed that skin pigmentation is controlled by 3 to 4 gene pairs (e.g., A, B, C). A genotype of AABBCC produces very dark skin, aabbcc produces very light skin, and AaBbCc produces an intermediate (mulatto) shade.
  • Human Stature (Height): Controlled by over 400 genes, alongside environmental factors.
  • Dermatoglyphics: Total Finger Ridge Count (TFRC) is a classic polygenic trait minimally affected by the environment.

Polygenic vs. Multifactorial When a polygenic trait is significantly influenced by environmental factors (nutrition, climate, disease), it is termed Multifactorial Inheritance. For instance, genetic potential dictates maximum height, but childhood nutrition determines the actual height achieved.

Anthropological Significance Understanding polygenic inheritance is crucial for physical anthropology because it dismantles the biological concept of "Race." It proves that human traits vary in a continuous gradient (clines) across geographical regions, adapting to local environments, rather than existing in bounded, typological racial categories.

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? 2026 Why the classifications of Indian populations, based on somatometric and somatoscopic characteristics failed to develop a common understanding of the population diversity? 2026 Canalization and catch-up growth. 2026 Genetic polymorphism and natural selection.

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UPSC Anthropology Optional 2023 — Paper I

28 questions

1(b) Cultural impact of Iron Age

10 Marks150 words
Syllabus: Paper I > 1.8(b) Cultural Evolution > Iron Age
2023Paper IPrehistoric ArchaeologyModel answer available

1(e) Gene expression

10 Marks150 words
Syllabus: Paper I > 1.7 The biological basis of life > Gene and protein synthesis
2023Paper IHuman Genetics & Human BiologyModel answer available

5(c) Glottochronology

10 Marks150 words
Syllabus: Paper I > 7. Culture, language and communication > Language change
2023Paper ICulture & SocietyModel answer available

5(d) Menopausal symptoms

10 Marks150 words
Syllabus: Paper I > 11.1 Relevance of menarche, menopause and other bio-events to fertility
2023Paper IHuman Genetics & Human BiologyAnswer coming soon

5(a) Polygenic Inheritance

10 Marks150 words
Syllabus: Paper I > 9.2 Mendelian genetics in man > Polygenic inheritance
2023Paper IHuman Genetics & Human BiologyModel answer available

1(c) Race and Ethnicity

10 Marks150 words
Syllabus: Paper I > 9.5 Race and racism > Race and ethnicity
2023Paper IHuman Genetics & Human BiologyModel answer available

5(e) William Ogburn and Cultural lag

10 Marks150 words
Syllabus: Paper I > 6. Anthropological Theories > Cultural lag (Ogburn)
2023Paper IAnthropological TheoriesModel answer available