Population genetics

Population genetics is the branch of genetics which studies the genetic composition of populations. It brings together genetics, evolution, natural selection, breeding, statistics and mathematics. Mathematical and computer models are produced, and field research is done to test the models.
A brief history.
Starting, perhaps, with G. Udny Yule's paper in 1902, population theorists tackled key issues in genetics and evolution. G.H. Hardy and Wilhelm Weinberg showed that if a population had random mating, no selection, migration or mutation, then the proportion of alleles would remain the same generation after generation. This was the Hardy–Weinberg law, the first great result of this new field of research.
Population genetics made great progress from 1918 to 1937. During this period, Ronald Fisher, J.B.S. Haldane and Sewall Wright worked on the connection between evolution and genetics, using new mathematical techniques, such as statistical probability. E.B. Ford and Theodosius Dobzhansky did field research on the genetics of natural populations of lepidoptera and "Drosophila", respectively. Broadly speaking, this work proved that the newly rediscovered Mendelian genetics could be reconciled with Darwinian evolution. This laid the groundwork for the modern evolutionary synthesis, which took place in the following years, from about 1937 to 1953.
In the second half of the 20th century, population geneticists tackled a range of complex evolutionary problems, such as the evolution of sex, sexual selection, kin selection (altruism), mimicry and molecular evolution. The key figures included John Maynard Smith, Motoo Kimura and William Hamilton. Techniques developed for population genetics help to decide what contribution heredity and environment make in developmental biology.
Genetic hitch-hiking and selective sweep.
These concepts apply when a mutation is strongly favoured and "pulls along" nearby genes on its chromosome. The genes pulled along are genes which are previously under little selection. In a selective sweep, positive selection causes the new mutation to reach "fixation" (be the only allele present at that locus in all members of the population) so quickly that linked alleles can "hitchhike" and also become fixed. Evidence is growing that this effect does happen.