evolution of population Flashcards
a localized group of individuals capable of interbreeding and producing fertile offspring
population
change in allele frequencies in a population over generations
microevolution
three mechanisms cause allele frequencies change:
-natural selection
-genetic drift (chance events that alter allele frequencies)
-gene flow (the transfer of alleles between populations)
differences among individuals in the composition of their genes or other DNA sequences
genetic variation
the product of inherited genotype and environmental influences
phenotype
can only act on variation with a genetic component
natural selection
can be classified on an either-or basis
discrete characters
vary along an continuum within a population
quantitative characters
measures the average percent of loci that are heterozygous in a population
average heterozygosity
measured by comparing the DNA sequences of pairs of individuals
nucleotide variability
a change in the nucleotide sequence of an organism’s DNA
mutation
differences between gene pools of separate populations
geographic variation
graded change in a trait along a geographic axis
cline
consists of all the alleles for all loci in a population
gene pool
fixed if all individuals in a population are homozygous for the same allele
locus
states the frequencies of alleles and genotype in a population remain constant from generation to generation
Hardy-Weinberg principle
The five conditions for nonevolving populations are rarely met in nature:
-No mutations
-Random mating
-No natural selection
-Extremely large population size
-No gene flow
describes how allele frequencies fluctuate unpredictably from on generation to the next
genetic drift
occurs when a few individuals become isolate from a larger population
founder effect
is a sudden reduction in population size due to a change in the environment
bottleneck effect
effects of genetic drift: a summary
-significant in small populations
-causes allele frequencies to change at random
-can lead to a loss of genetic variation w/in populations
-can cause harmful alleles to become fixed
consists of the movement of alleles among populations
gene flow
is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
relative fitness
favors individuals at one end of the phenotypic range
directional selection
favors individuals at both extremes of the phenotypic range
disruptive selection
favors intermediate variants and acts against extreme phenotypes
stabilizing selection
natural selection for mating success
sexual selection
marked differences between the sexes in secondary sexual characteristics
sexual dimorphism
is a competition among individuals of one sex (often males) for mates of the opposite sex
intrasexual selection
often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates
intersexual selection
is genetic variation that does not confer a selective advantage or disadvantage
neutral variation
occurs when natural selection maintains stable frequencies of 2+ phenotypic forms in a population
balancing selection
when heterozygotes have a higher fitness than do both homozygotes
heterozygote advantage
the fitness of a phenotype declines if it becomes too common int he population
frequency- dependent selection
why natural selection cannot fashion perfect organisms
-selection can act only on existing variations
-evolution is limited historical constraints
-adaptations are often compromises
-chance, natural selection, and the environment interact
