Gene pools and allele frequencies

Gene pools and allele frequenciesSpec D4.1.9, D4.1.10, D4.1.11

Gene pool

All the genes and their different alleles present in a population.

Allele frequency

The proportion of all copies of a gene in a population that are a particular allele, given as a value from 0 to 1.

Geographically isolated populations

When populations are geographically isolated, alleles do not flow between them. Different mutations arise, selection pressures differ, and chance events change allele frequencies, so the gene pools diverge.

• Lactase persistence (digesting lactose as an adult): over 90% of people in Sweden and Denmark have it, and it is common in some pastoralist groups in East Africa, but rare (5% or less) in most East Asian populations. Different lactase-persistence alleles (different mutations near the lactase gene) are responsible in Europe and in East Africa.
• ABO blood groups: the Iᴮ allele is most frequent in Central and South Asia, while many Indigenous populations of South America have almost only the i allele (blood group O).

Natural selection changes allele frequencies

Individuals differ in their heritable traits. Those with traits giving higher fitness leave more offspring, so the alleles for those traits make up a larger share of the next generation's gene pool. Evolution can therefore be described as a change in allele frequency in a gene pool over time.

Darwin developed the theory of evolution by natural selection without knowing about genes. Biologists later integrated genetics with natural selection in what is now known as neo-Darwinism.