Allele frequencies & Population genetics

Population

Local groups of organisms belonging to a single species, sharing common gene pool

Gene pool

Set of genetic information carried by the members of a sexually reproducing population

Allele frequencies

Frequency with which particular alleles of a gene are present in a population

How allele frequency is measured

Directly and hardy-Weinberg equation

How are recessive allele frequencies measured?

With the Hardy-Weinberg mathematical equation

What assumptions must be met in the Hardy-Weinberg law for allele and genotype frequency to stay constant from generation to generation

Population is large enough so there are not error in measuring allele frequency, all genotypes are equally able to reproduce, mating in the population is random, other factors that change allele frequency (mutation and migration) can be ignored

In the Hardy-Weinberg law, p2 stands for..

Frequency of homozygous dominant genotypes

In the Hardy-Weinberg law, 2pq stands for..

frequency of heterozygous genotype in the population

In the Hardy-Weinberg law, q2 stands for..

Frequency of homozygous recessive genotypes

In the Hardy-Weinberg law, 1 stands for..

new genotypes in generation

Genetic equillibrium

Allele frequency for particular gene remain constant from generation to generation. Explains why dominant alleles do not replace recessive alleles.

What 3 things can the Hardy-Weinberg equation be used for?

Estimate frequency of autosomal dominant and recessive alleles in a population, detect when allele frequency are shifting in a population, measure the frequency of heterozygous carriers of deleterious recessive alleles in a population

Explain the 5 reasons that the Hardy-Weinberg equation mostly doesn’t occur.

Non-random changes to allele frequency (religious reasons, isolated populations), Populations wiped out by war, natural disaster, some people have more kids, travel & immigration alter alleles available in pool, new mutations

What may change allele frequency

Genetic drift

Genetic drift

Random fluctuations from generation to generation that take place in small isolated populations like isolated populations

What are two factors that accelerate genetic drift?

Founder effect and population bottleneck

Founder effect

Small group leaves population to start new settlement, and the new colony has different allele frequency than original population

Population bottleneck

When members of a group die, and only a few are left to regrow the population. An allele in the remaining population that survived catastrophe may become more common in the replenished population because the gene pool became more restricted

Negative artificial selection

Trait selected against and removed from the population - early death before reproduction

Positive artificial selection

Trait confers an advantage and is selected for in a population through increase survival or number of offspring

Theories on how and where homo sapiens originated

Out of Africa (supported by genetic evidence)

Multiregional hypothesis (supported by fossil records)