1What are three main types of selection?
directional, stabilizing and disruptive selection
2directional selection
occurs when an extreme phenotype is favored
3stabilizing selection
occurs when an intermediate phenotype is favored; individuals near the average are favored
4disruptive selection
two or more extreme phenotypes are favored over any intermediate phenotype; incomplete dominance: sometimes the heterozygote stands out
5sexual selection
adaptive changes in males and females that lead to an increased ability to secure a mate
6heterozygote advantage
indviduals with two different alleles have greater fitness than homozygous individuals
7balanced polymorphism
two different versions of a gene are maintained in a population by natural selection (favors heterozygotes)
8example of imperfect adaptations
walking upright puts stress on the spine, but there is more selective pressure to walk upright
9gene pool
alleles for all the genes within a population
10What does a change in allele frequency mean?
evolution is occuring
11What must be true in order to keep the allele frequencies from changing?
Hardy-Weinberg principle: 1. no mutations 2. no gene flow 3. random mating 4. no genetic drift 5. no selection
12How does gene flow help a species recover from genetic drift?
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)
13How does gene flow prevent speciation?
it can reduce differences among populations
14microevolution
small measurable evolutionary changes within a population from generation to generation
15causes of microevolution
genetic mutation, gene flow, nonrandom mating, genetic drift, natural selection
16genetic mutations
ultimate source for allele differences. ex: freckles
17gene flow
movement of alleles among populations by migration of breeding individuals
18nonrandom mating
selection of mate according to genotype of phenotype (certain genes are favorred)
19assortative mating
tend to mate with individuals with the same phenotype
20genetic drift
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)
21bottleneck effect
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)
22founder effect
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