Changing Allele FrequenciesChanging Allele Frequencies

Allelic Frequencies Change When Allelic Frequencies Change When There Is:There Is:

Non-random matingNon-random mating

Gene flow/MigrationGene flow/Migration

Genetic driftGenetic drift

MutationMutation

Natural selectionNatural selection

Non-random MatingNon-random Mating

We marry people similar to ourselves 80% of the timeWe marry people similar to ourselves 80% of the time1/3 of all marriages occur between people who were 1/3 of all marriages occur between people who were born <10 miles apartborn <10 miles apartCertain individuals contribute more to the next Certain individuals contribute more to the next generation than othersgeneration than others– Prize bull semenPrize bull semen– Chinese immigrant to South African with rare dominant mutation Chinese immigrant to South African with rare dominant mutation

that causes teeth to fall out by age 20 had 7 wivesthat causes teeth to fall out by age 20 had 7 wives– Albinism in Hopi IndiansAlbinism in Hopi Indians– Genocide by rape in DarfurGenocide by rape in Darfur– Consanguinuity (a.k.a. inbreeding)Consanguinuity (a.k.a. inbreeding)– Endogamy =marriage within a communityEndogamy =marriage within a community

Non-random MatingNon-random Mating

Gene Flow/MigrationGene Flow/Migration

Individuals may join the migrationIndividuals may join the migration

Individuals may mate within other populations Individuals may mate within other populations along the wayalong the way

Immigrants introduce alleles and emigrants Immigrants introduce alleles and emigrants remove themremove them

A A clinecline exists when neighboring populations exists when neighboring populations have differing allelic frequencieshave differing allelic frequencies– Geographical barriers (Geographical barriers (e.ge.g. mountains). mountains)– Language barriersLanguage barriers

Gene Flow/MigrationGene Flow/Migration

Genetic DriftGenetic Drift

Chance sampling of alleles from the whole Chance sampling of alleles from the whole populationpopulation

Due to:Due to:– Founder effectFounder effect– Population bottleneckPopulation bottleneck

Founder EffectFounder Effect

Small group leaves the population to start Small group leaves the population to start a new settlementa new settlementNew colony may have different allele New colony may have different allele frequencies than the original populationfrequencies than the original populationEx: Small religious sect community in Ex: Small religious sect community in Utah/Arizona Utah/Arizona – Founded by 2 individuals in the 1930’sFounded by 2 individuals in the 1930’s– 50% of all fumarate deficiency50% of all fumarate deficiency

Mental retardation, seizures, coma Mental retardation, seizures, coma

Population BottleneckPopulation Bottleneck

Many members of a population die and only a Many members of a population die and only a few are left to re-populatefew are left to re-populate

Much more restricted gene pool than original Much more restricted gene pool than original populationpopulation

Ex: Pingalapese people of the East Caroline Ex: Pingalapese people of the East Caroline Islands in MicronesiaIslands in Micronesia– Typhoon wiped out all but 9 males and 10 femalesTyphoon wiped out all but 9 males and 10 females– Autosomal recessive achromatopsia very prevalentAutosomal recessive achromatopsia very prevalent

Color-blindnesss, nearsightedness, and cataractsColor-blindnesss, nearsightedness, and cataracts

Genetic DriftGenetic Drift

MutationMutation

Major and continual source of genetic Major and continual source of genetic variationvariation

One allele changes into anotherOne allele changes into another

Must occur in gamete in order to affect Must occur in gamete in order to affect future generations and allele frequenciesfuture generations and allele frequencies

Genetic LoadGenetic Load

Mutations that lead to lethal traits are often Mutations that lead to lethal traits are often eliminated from the gene pool, however, eliminated from the gene pool, however, some mutant alleles can persist in some mutant alleles can persist in heterozygotesheterozygotes

Genetic load refers to the collection of Genetic load refers to the collection of these deleterious alleles in the populationthese deleterious alleles in the population– Each of us has 5-10 recessive lethal allelesEach of us has 5-10 recessive lethal alleles

MutationMutation

Natural SelectionNatural Selection

Guided by changes in the environmentGuided by changes in the environment

Individuals with certain phenotypes are Individuals with certain phenotypes are more likely to survive and have more likely to survive and have reproductive successreproductive success

Ex: Antibiotic resistanceEx: Antibiotic resistance– Antibiotics select for those bacteria which are Antibiotics select for those bacteria which are

antibiotic-resistantantibiotic-resistant

Natural SelectionNatural Selection

Forces that Alter Allele Forces that Alter Allele Frequencies