医学遗传学-08基因的群体行为英语.pptVIP

08基因变异的群体行为 Population Genetics What is a population from a genetic perspective? A population in the genetic sense, is not just a group of individuals, but a breeding group The genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one generation to the next. In the transmission the genotypes of the parents are broken down and a new set of genotypes is constituted in the progeny, from the genes transmitted in the gametes. The genes carried by the population thus have continuity from generation to generation, but the genotypes in which they appear do not. The genetic constitution of a population, referring to the genes it carries, is described by the array of gene frequencies, that is by specification of the alleles present at every locus and the numbers or proportions of the different alleles at each locus. Goals of Population Genetics To describe how the frequency of an allele which controls a trait changes over time； To analyze the factors that lead to changes in gene (allele) frequencies； To determine how changes in gene (allele) frequencies affect evolution and speciation. Why Study Populations and Gene Frequencies Genetic variability necessary for evolutionary success; Measuring genetic variability at many loci can characterize a population; Variability of phenotypic and molecular traits are analyzed. 1. Variability and Gene (or Allelic) Frequencies Genetic data for a population can be expressed as gene or allelic frequencies; All genes have at least two alleles; Summation of all the allelic frequencies for a population can be considered a description of the population; Frequencies can vary widely among the alleles in a population; Two populations of the same species do not have to have the same allelic frequencies. Genotypic frequencies It describes the distribution of genotypes in a population. Example