Chapter 3 Population Genetics for Large Populations

The diversity of life is a fundamental empirical fact of nature. Casual observation alone confirms the great variety of species. But diversity also prevails within single species. As in human populations, the individuals of a species vary considerably in their outward traits—size and shape, external markings, fecundity, disease resis-tance, etc. This is called phenotypic variation, and, since phenotypes are shaped by genes, it reflects an underlying, genotypic diversity. The achievements of genetics and molecular biology, as described in Chapter 1, have allowed us to measure and confirm the genotypic variability of populations down to the molecular level. The science of genotypic variation in interbreeding populations is called popu-lation genetics. Its goal is understanding how genetic variation changes under the influence of selection, mutation, and the randomness inherent in mating, as one generation succeeds another. To achieve this, population geneticists combine what is known about the mechanisms of heredity—how DNA carries genetic information, how chromosomes function and give rise to Mendel’s laws, how mutations arise— with hypotheses about mating and selective advantage, to propose mathematica