Revision summary
Segregation and independent assortment are the core Mendelian laws. Human pedigrees of recessives, dominants, and X-linked traits apply them. Hardy–Weinberg is Mendelism at population scale. Consanguinity and caste mating violate random-mating assumptions. Polygenic traits and eugenic history are the critique.
Model answer
Introduction
Mendel’s principles explain how discrete traits move from parents to offspring. In human populations they work, and they need Hardy–Weinberg, linkage, and culture before they become demography.
Body
The principles
- Segregation: alleles of a locus separate in gametes. Independent assortment: unlinked loci mix independently.
- Dominance is a phenotypic relation, not a moral one. Recessive traits hide in heterozygotes.
- Mendel used peas. Humans added sex linkage, as in haemophilia, and mitochondrial exceptions.
Application to human populations
- Pedigrees for albinism, PTC, achondroplasia, and thalassaemia are Mendelian teaching files.
- Hardy–Weinberg turns Mendel into population frequencies if mating is random and selection is nil.
- Consanguinity, studied by Sanghvi in India, raises homozygosity for recessives.
- Blood groups applied Mendelism at scale. Forensic STRs still assume Mendelian transmission.
Critical limits
- Most stature and skin traits are polygenic, not one-pea genes.
- Linkage, imprinting, penetrance, and phenocopies break textbook ratios.
- Culture decides who mates. Caste and village endogamy are not bean-bag random mating.
- Eugenic misuse of Mendelism was political. Counselling today is voluntary and case-based.
Flow diagram
flowchart TD MEN[Mendel segregation assortment] --> PED[Human pedigrees] PED --> HW[Hardy Weinberg] HW --> LIM[Polygenic consanguinity culture]
Conclusion
Mendelian principles still govern single-locus human traits and forensic markers. Population application needs Hardy–Weinberg plus a map of marriage. Polygenic and cultural facts stop a pea-garden view of whole peoples.
Quick related
Students also ask
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Explain the significance of screening and counseling for genetic disorders.
Next question in the 2016 paper (Q7). View answer →
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Do all human traits Mendelise?
Single-locus diseases often do. Height and behaviour usually do not.
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Is independent assortment always true?
No. Linked genes on one chromosome travel together until recombination.
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