Chapter 14
Population Genetics 2- Changing Allele frequencies

Allele frequencies can change creating microevolution

Individuals of one genotype reproduce more often with each other

Individuals migrate between populations

Population size is small or a group becomes reproductively isolated within a larger population

Mutation introduces new alleles or new copies of alleles

Individuals with a particular genotype are more likely to have viable, fertile offspring

Hardy-Weinberg Equilibrium

A condition in which allele frequencies remain constant is called Hardy-Weinberg equilibrium

Application of Hardy-Weinberg Equilibrium:
calculating risk

Carrier Frequency for Cystic Fibrosis

Application of Hardy-Weinberg Equilibrium:
DNA identification

Application of Hardy-Weinberg Equilibrium:
DNA identification

the DNA pattern observed from the population is calculated using the  frequency of alleles in that population.

Genotype frequencies of unlinked loci are multiplied.

Allele frequencies vary in different populations.  Use of correct population information is important.

Allele frequencies can change creating microevolution

Individuals of one genotype reproduce more often with each other

Individuals migrate between populations

Population size is small or a group becomes reproductively isolated within a larger population

Mutation introduces new alleles or new copies of alleles

Individuals with a particular genotype are more likely to have viable, fertile offspring

Nonrandom mating

    Random mating occurs when individuals of one genotype mate randomly with individuals of all other genotypes.

    Nonrandom mating indicates individuals of one genotype reproduce more often with each other

 

Ethnic or religious preferences

Isolate communities

Worldwide, 1/3 of all marriages are between people born within 10 miles of each other

Cultures in which consanguinity is more prominent

Consanguinity is marriage between relatives

    e.g. second or third cousins

Migration

   When people move, their genes go with them. 

   The genetic effects of migration are reflected in current populations.

 

   Allele frequencies change when alleles are disproportionately distributed in the migrants.

Migration

Changes in allele frequency can be mapped across geographical or linguistic regions.

Allele frequency differences between current populations can be correlated to certain historical events.

Mapping a trait geographically can suggest patterns of migration

Frequencies of galactokinase deficiency decrease westward from home of the Viax Roma in Bulgaria.

 

Gradients in allele frequencies between successive neighboring  populations are called clines.

 

Genetic Drift

    Changes in allele frequency occur when gametes do not reflect the allele frequencies in parents by random chance. 

 

This random sampling error is called genetic drift.

 

Genetic drift is more pronounced in small populations.

Genetic Drift

   Events that create small populations enhance the effect of genetic drift.

 

Founding a new population

Bottlenecks (natural disaster, famine)

Geographic separation (islands)

Linguistic differences

Genetic Drift

    Founder effects refer to the genetic impact of starting a new population from a relatively small group of people.

 

Mutation can introduce new alleles.

Mutation can convert one allele to another.

 

Mutation has a minor impact unless coupled with another effect (small population size, selection).

Mutation

Allele frequencies change in response to mutation.

 

Natural Selection

The differential survival and reproduction of individuals with a particular phenotype is called natural selection.