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Home/Anthropology/Mains PYQ/2024/Paper I/Human Genetics & Human Biology
UPSC MainsAnthropology Optional Paper I 2024 15 Marks Model Answer Available

Multifactorial Traits in Man — 2024 Paper I

Question · 2024 · Paper I · 15 Marks

What is a multifactorial trait? Illustrate your answer with suitable human examples.

Model Answer

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Introduction

A multifactorial trait is a phenotypic characteristic produced by the combined action of several genes and environmental factors. Unlike a Mendelian trait controlled mainly by a single gene, it does not follow definite dominant–recessive ratios.

Its expression may be represented as:

Phenotype = Genetic effects + Environmental effects + Gene–environment interaction

Characteristics

  • Several genes contribute small cumulative effects.
  • Environmental factors modify the genetic potential.
  • The trait commonly shows continuous variation in a population.
  • It tends to cluster in families but does not follow simple Mendelian inheritance.
  • Its expression and heritability may differ across populations and environments.

Human Examples

Stature

Height is controlled by numerous genes influencing skeletal growth and hormones. Nutrition, childhood illness and living conditions determine whether an individual attains the genetically possible height.

Skin pigmentation

Genes regulating melanin production produce inherited differences in pigmentation, while exposure to ultraviolet radiation causes tanning. It therefore reflects both polygenic inheritance and environmental modification.

Body weight and obesity

Genes affect appetite, metabolic rate and fat storage. Their expression is modified by diet, physical activity, occupation and lifestyle.

Blood pressure

Hypertension develops through the interaction of genetic susceptibility with salt intake, obesity, stress, ageing and physical inactivity.

Type 2 diabetes

Multiple genes influence insulin production and glucose metabolism, while obesity, diet and sedentary behaviour increase the probability of disease.

Multifactorial Threshold Traits

Some multifactorial traits appear as distinct categories rather than continuous variation. According to D. S. Falconer’s threshold model, every individual possesses an underlying liability. The disorder appears only when genetic and environmental liability crosses a critical threshold.

Examples include:

  • cleft lip and palate;
  • neural-tube defects;
  • congenital pyloric stenosis;
  • certain forms of coronary heart disease.

The risk is generally greater among close relatives, in severe cases and where more family members are affected.

Conclusion

Multifactorial traits demonstrate that human variation cannot be explained through heredity or environment in isolation. They result from continuous interaction between biological inheritance and developmental, ecological and socio-economic conditions, making them important in human genetics, epidemiology and preventive medicine.

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 2024 — Paper I

28 questions

1(a) Attributes of culture

10 Marks150 words
Syllabus: Paper I > Nature of Culture > Characteristics of Culture > Attributes of culture
2024Paper ICulture & SocietyModel answer available

5(d) Authority and forms of political organization

10 Marks150 words
Syllabus: Paper I > Political Organization and Social Control > Power, Authority and Legitimacy > Band, tribe, chiefdom, state
2024Paper IEconomic & Political AnthropologyModel answer available

5(a) Chronometric dating

10 Marks150 words
Syllabus: Paper I > Prehistoric Archaeology > Chronology and Dating > Chronometric (absolute) dating methods
2024Paper IPrehistoric ArchaeologyModel answer available

5(b) Cultural relevance of the Kula

10 Marks150 words
Syllabus: Paper I > Economic Organization > Reciprocity and Exchange > Kula ring
2024Paper IEconomic & Political AnthropologyModel answer available

1(b) Harappan maritime trade

10 Marks150 words
Syllabus: Paper I > Prehistoric Archaeology > Chalcolithic and Bronze Age > Harappan civilization; maritime trade
2024Paper IPrehistoric ArchaeologyModel answer available

1(e) Hemoglobin in health and disease

10 Marks150 words
Syllabus: Paper I > Human Genetics > Genetic Polymorphism > Haemoglobinopathies; health and disease
2024Paper IHuman Genetics & Human BiologyModel answer available

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