A population is all the members of the same species that live in one loaction. Case 4: genetic drift j a change in allele frequency within a population that occurs porely as a result of chance~ Genetic drift will cause polulation to lose their heterozygotes, and to become comprised entirely of homozygous individuals. Founder effect j only the alleles of the founding individuals are passed to next generation. Populations that are initially large and then are reduced dramatically in size are said to have passed through a population bottleneck. Mutation j a permanent change in the sequence of dna. T although physcial abnormalities result from some kind of mutation, most of them have no effect about the phenotype. T occur during the peocess of dna replication j errors: substiturion of one nucleotide, insertion or deletion of a nucleotide bas j point mutation. Chromosomal or structural mutation jsmall segment of dna can be deleted, duplicated, inverted or translated.