AP Biology Chapter 23


Terms in this set (...)

evolution on its smallest scale
genetic variation
differences among individuals in the composition of their genes or other DNA sequences
neutral variation
differences in DNA sequences that do not confer s selective advantage or disadvantage, usually a result of point mutations in noncoding regions
formation of genetic variation
formation of new alleles, altering gene number of position, rapid reproduction, sexual reproduction
a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
gene pool
all copies of every type of allele at every locus in all members of the population
Hardy-Weinberg equilibrium
a population that isn't evolving
conditions for Hardy-Weinberg equilibrium
No mutations, random mating, no natural selection, extremely large population size, no gene flow
adaptive evolution
evolution that results in a better match between organisms and their environment (caused by natural selection)
genetic drift
allele frequencies fluctuating unpredictable from one generation to the next, especially in small populations
founder effect
when individuals separate from the population, the smaller group may establish a new population whose gene pool differs from the source population. The larger population (the source) will not be effected by genetic variation
bottleneck effect
a severe drop in population which results in an overrepresented allele an underrepresented allele
Effects of genetic variation
genetic drift is significant in small populations, genetic drift can cause allele frequencies to change at random, genetic drift can lead to a loss of genetic variation within populations, genetic drift can cause harmful alleles to become fixed
Gene flow
the transfer of alleles into or out of a population due to the movement of retile individuals or their gametes
relative fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
directional selection
occurs when conditions favor individuals exhibiting one extreme of a phenotype range, thereby shifting a population's frequency curve for the phenotypic character in one direction or the other. Common when a population changes or members migrate
Disruptive selection
occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
Stabilizing selection
acts against extreme phenotypes and favors intermediate variants
sexual selection
a form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates
sexual dimorphism
a diference in secondary sexual characteristics between males and females of the same species. a result of sexual selection
intrasexual selection
selection within the same sex. individuals of one sex compete directly for mates of the opposite sex. most common among males
intersexual selection
also called mate choice; individuals of one sex (usually females) are choosy in selecting their mates from the other sex. It usually depends of the showiness of the male's appearance or behavior
balancing selection
natural selection that maintains two or more phenotypic forms in a population
heterozygote advantage
if individuals who are heterozygous at a particular locus have a greater fitness than do both kinds of homozygotes, they exhibit heterozygote advantage
frequency-dependent selection
the fitness of a phenotype depends on how common it is in the population
Why can't natural selection fashion perfect organisms?
1. Selection can act only on existing variations. New advantageous alleles do not arise on demand.
2. Evolution is limited by historical constraints. New structures aren't formed, but instead evolution adapts to the existing structures.
3. Adaptations are often compromises. We can be versatile and athletic but our limbs are prone to sprains.
4. Chance, natural selection, and the environment interact. Alleles are sometimes "left behind" or the organism lives in a constantly changing environment