ch23 the evolution of populations
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the total aggregate of genes in a population at any one time.
small changes in allele frequencies
-Evolutionary change below the species level; change in the allele frequencies in a population over generations.
the hardy weinberg theorem
= if nothing external acts upon a gene pool, the allele frequencies remain constant.(so, no evolution)
- The principle that frequencies of alleles and genotypes in a population
- remain constant from generation to generation, provided that only
- Mendelian segregation and recombination of alleles are at work.
- rarely holds for many generations in nature. because 5 condidtions must be met:
- -big pop. size
- -no gene flow
- -no mutations
- -random mating
- -no natural selection
- (the opposites of these change allele frequencies --> cause evolution)
=random changes in allele frequencies that can occur in small populations
drift thens to reduce variation because some alleles disappear.
bottle neck effect
= pop. could become small due to disaster
=when a few individuals colonize a new habitat
=individuals or gametes entering or leaving the pop.
tends to reduce differences between pop's
relative contribution an individual makes to gene pool of the next generation.
ways in which natural selection changes pop.s
- -directional selection:pop. changes in response to changing environment
- -disruptive selection:condition favour individuals at extreme of phenotypic range
- -stabilizing selection:continues to remove extreme phenotype.
=when certain phenotypes increase fitness because they increase reproductive success.
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