How Populations Evolve Genetic Variation within a Population is due to: Mutations Recombination of Genes Crossing over in Meiosis

gene pool – the combined alleles of all of the individuals in a population; genetic variation is stored in a population’s gene pool allele frequency- a measure of how common a certain allele is in the population

The Hardy-Weinberg Principle: states that the frequencies of alleles in a population do not change unless evolutionary forces act on the population. the principle holds true for any population as long as the population is large enough that its members are not likely to mate with relatives and as long as evolutionary forces are not acting

Five Principle Evolutionary Forces: gene mutation – a change in the DNA sequence; mutation rates in nature are very slow and not all mutations result in phenotypic changes gene flow – the movement of alleles into or out of a population; occurs because new individual (immigrants) add alleles to the population and departing individuals (emigrants) take alleles away

nonrandom mating– occurs when individuals prefer to mate with others that live nearby or are of their own phenotype genetic drift – occurs in small populations, the frequency of an allele is greatly changed by a chance event such as a fire or landslide; the loss of even one individual from the population can have major effects on the allele’s frequency

5. natural selection – the frequency of the allele will increase or decrease depending on the allele’s effects on survival and reproduction; natural selection is one of the most powerful agents of genetic change

Speciation Through Isolation: Speciation – the formation of new species as a result of evolution by natural selection Reproductive Isolation – when members of a population can no longer mate successfully Behavioral Isolation – differences in courtship or mating behaviors Geographical Isolation – physical barriers such as rivers, mountains, and dry lakebeds that separate a population Temporal Isolation – when timing prevents reproduction between populations