遗传学精品教学（南京大学）Chapter 7 population genetics.pptVIP

POPULATION GENETICS Study of evolution from a genetic point of view What is a population? A collection of individuals of the same species that routinely interbreed ( living in the same location) A species is a naturally breeding group of organisms that produce fertile offspring. A population is the smallest in which evolution occurs POPULATION GENETICS Definition: Study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space. As such, it attempts to explain such phenomena as adaptation and speciation Three parameters to keep in mind: Allele frequency: the proportion of a specific allele at a given locus, considering that the population may contain from one to many alleles at that locus Genotype frequency: the proportion of a specific genotype at a given locus, considering that many different genotypes may be possible. Phenotype frequency: the proportion of individuals in a population that exhibit a given phenotype. The gene pool (allele pool) The gene pool (allele pool) consists of all the alleles at all the loci in the population. Hardy-Weinberg Equilibrium Conditions No net mutation, No migration NO sex selection Large population size Mating is random Natural selection does not occur What is Hardy-Weinberg Equilibrium? Assumes NO evolution occurs. All 5 conditions must be meet. Can never happen! It is a model or a yardstick to measure how much a population or species has evolved. Hardy-Weinberg Equilibrium The allele frequency in a population can be calculated using the Hardy-Weinberg equation. This equation states that all of the allele combination must add to ONE (1) Dominate alleles + recessive alleles = 1 p + q = 1 The frequency of the heterozygote may also be calculated Disruption of Genetic Equilibrium Mutation Migration Genetic Drift Non- Random Mating Natural