ch23 the evolution of populations

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.

= 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.

= 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.

• -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.