chp 15: evolution on small scale

directional, stabilizing and disruptive selection

occurs when an extreme phenotype is favored

occurs when an intermediate phenotype is favored; individuals near the average are favored

two or more extreme phenotypes are favored over any intermediate phenotype; incomplete dominance: sometimes the heterozygote stands out

adaptive changes in males and females that lead to an increased ability to secure a mate

indviduals with two different alleles have greater fitness than homozygous individuals

two different versions of a gene are maintained in a population by natural selection (favors heterozygotes)

walking upright puts stress on the spine, but there is more selective pressure to walk upright

alleles for all the genes within a population

evolution is occuring

Hardy-Weinberg principle: 1. no mutations 2. no gene flow 3. random mating 4. no genetic drift 5. no selection

it introduces new genes to a new population which may help a species that has limited genes as a result from a natural disaster (bottleneck) or being isolated (founder)

it can reduce differences among populations

small measurable evolutionary changes within a population from generation to generation

genetic mutation, gene flow, nonrandom mating, genetic drift, natural selection

ultimate source for allele differences. ex: freckles

movement of alleles among populations by migration of breeding individuals

selection of mate according to genotype of phenotype (certain genes are favorred)

tend to mate with individuals with the same phenotype

refers to changes in the allele frequencies of a gene pool due to chance (ex: happening to run over a bunch of ants because htey were in your walking path)

species suffers a near extinction and only a few survivors go on to produce the next generation. ex: cheetahs who have extreme similarity (type of genetic drift)

rare alleles occur at a higher frequency in a population isolated from the general population. ex: the amish are more likely to carry a recessive gene for dwarfism and polydactylism