Revision summary
Polygenic traits are built by many loci of small effect. Fisher joined Mendelism to Galton’s continuous curves. Nilsson-Ehle’s wheat colour is the classic additive model. Human stature and skin colour are standard anthropological examples. GWAS still finds many tiny effects, not a racial master gene.
Model answer
Introduction
Polygenic inheritance is the passing of a trait that many loci of small effect build together. The result is a curve of people, not a 3:1 garden of peas.
Body
The genetic idea
- R. A. Fisher showed that many Mendelian loci plus environment can produce the continuous distributions that Francis Galton had measured for stature.
- Nilsson-Ehle’s wheat-kernel colour is the teaching plant model: add more contributing alleles and the colour darkens by steps that look smooth in a large sample.
- Human stature, skin colour, blood pressure, and many disease risks sit in this architecture, which is why they are also called multifactorial when environment is counted.
Anthropological use
- Skin colour is a polygenic cline with latitude and ultraviolet light, not a three-race switch, which is why Livingstone and later geneticists rejected racial typology for this trait.
- Twin and family studies estimate heritability, but a heritability figure is not a gene list and is not destiny across environments.
- Genome-wide association studies now name many loci of tiny effect, which confirms the old polygenic picture without restoring Mendelian race types.
Flow diagram
flowchart TD L[Many loci] --> Q[Quantitative trait] E[Environment] --> Q Q --> H[Height skin colour]
Conclusion
Polygenic inheritance is many small loci making a quantitative trait. Anthropology needs it for stature, pigmentation, and complex disease, and it forbids treating those traits as single-gene races.
Quick related
Students also ask
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Prehistoric significance of Rakhigarhi
Next question in the 2023 paper (Q5). View answer →
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Is a polygenic trait non-Mendelian at each locus?
Each locus can still segregate. The phenotype looks non-Mendelian because many loci and the environment are summed.
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Can polygenic scores define races?
No. They describe statistical risk or stature inside samples. They do not restore biological races.
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