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22 Cards in this Set
- Front
- Back
Population
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unit of evolution
-group of organisms of the same species at a particular place at the same time |
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population genetics
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tracks the genetic makeup of populations over time
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Polymorphism
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genetic trait with distinct phenotypes
--when a population includes two or more forms of a phenotypic characteristic, the contrasting forms are called morphs |
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population genetics
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describing the genetic characteristics of populations
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gene pool
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all the genes in a population and their alleles
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hardy-weinberg equilibrium
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nonevolving population is in genetic equilibrium
-population's gene pool remains constant over time -frequencies of alleles (p and q) and genotypes (p2, 2pq, and q2) are unchanged |
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microevolution
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change in a population's frequencies of alleles
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sexual recombination
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results in most of the generation to generation variability in human populations
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Evolutionary forces that cause microevolution
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1. genetic drift
2. gene flow 3. mutation 4. natural selection |
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genetic drift
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random changes in allele frequencies due to sampling error in the production of gametes and fertilization
--changes are random and unpredictable (can't predict size/frequency) --important in small populations --genetic drift usually reduces genetic variation --the smaller the population, larger amount of genetic drift |
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special kinds of genetic drift
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bottleneck effect and founder effect
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bottleneck effect
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--genetic drift resulting from a drastic reduction in population size
--result of catastrophe --survivors only contain a portion of the genetic variation present before the bottleneck |
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founder effect
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small number of individuals leave a large population to colonize new, vacant habitat
--low variation --different frequencies than source (bigger) population |
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Gene flow
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the movement of alleles into or out of a population by migration
--reduces genetic differences between populations |
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mutation
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random changes in the DNA
-produces new alleles -source of genetic variation |
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natural selection (type of evolutionary forces for microevolution)
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consistently adaptive
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darwinian fitness
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contribution of an individual to the gene pool of the next generation relative to the contribution of the other individuals
-determined by genotype |
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3 general outcomes of natural selection
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1. directional selection
2. disruptive selection 3. stabilizing selection |
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directional selection
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-selection shifts curve directionally
-often results from environmental changes |
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diversifying/disruptive selection
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-selection against intermediate phenotypes
-can lead to different morphs being maintained in the population -often occurs when environment is patchy -different phenotypes favored in different patches |
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stabilizing selection
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-maintains a narrow range of phenotypes
-selection against extreme phenotypes -occurs in stable environments |
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things to note
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1. selection for some phenotypes and against otheres
2. evolutionary change occurs when the environment changes 3. genetic variation must be present for populations to respond to changes in selection |