________ evolve while _______ do not.
populations; individuals
Change in allele frequencies in a population over generations
microevolution
What are the three min mechanisms that can cause allele frequency change?
Natural selection, genetic drift, gene flow
differences among individuals in the composition of their genes or other DNA segments
genetic variation
The average percentage of loci that are heterozygous
average hetrozygosity
differences in the genetic compositions of separate populations
geographic variation
a graded change in character along a geographic axis
cline
Consists of all copies of every type of allele at every locus in all members of its population
gene pool
If only one allele exists for a particular locus in a population, that allele is said to be ____.
fixed
States that the frequencies of alleles and genotypes in a population will remain constant from generation to generation.
hardy Weinberg principal
what are the 5 hardy Weinberg conditions?
1.no mutations 2.random mating 3.no natural selection 4. extremely large population size 5. no gene flow
Chance events that can cause allele frequencies to fluctuate unpredictably from one generation to the next .
genetic drift
What are two examples of circumstances that can result n genetic drift?
fonder effect and bottle neck effect
When few individuals become isolated from larger population, this smaller group my establish a new population whose gene pool differs from the source population
founder effect
Sudden change in the environment, such a fire or flood, may drastically reduce the size of a population.
bottleneck effect
the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.
gene flow
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
relative fitness
occurs when conditions favor individuals exhibiting one extreme of a phenotypic range, thereby shifting a populations frequency curve for the phenotype character in one direction or the other.
directional selection
occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes.
disruptive selection
acts against both extreme phenotypes and favors intermediate variants.
stabilizing selection
A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
sexual selection
What can sexual selection result in?
sexual dimorphism
Difference between the two sexes in secondary sexual characteristics
sexual dimorphism
meaning selection within the same sex, individuals of one sex compete directly for mates of the opposite sex.
intrasexual
mate choice- individuals of one sex are choosy in selecting their mates from the other sex.
intersexual
differences in DNA sequence that do not confer a selective advantage or disadvantage.
neutral variation
occurs when natural selection maintains two or more forms in a population
balancing selection
if individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygous
heterozygote advantage
the fitness of a phenotype depends on how common it is in the population
frequency-dependent selection