Population Genetics Flashcards
Population genetics
quantitative study of the distribution of genetic variation in populations and how the frequencies of genes and genotypes are maintained or changed
Hardy-Weinberg principle
- applied to populations to estimate genotype frequencies in the population when allele frequency is known.
- If p is the frequency of allele A and q is the frequency of allele a in a gene pool:
- –The chance of an AA genotype is p2
- –The chance of an aa genotype is q2
- –Then chance of an Aa genotype is 2pq
Hardy-Weinberg equation
(p+q)2 = p2 + 2pq + q2
The Hardy-Weinberg is used to determine
the frequency of genotypes based on expressed phenotypes for autosomal recessive diseases
Phenotypes of homozygotes for recessive mutant alleles can be identified and their frequency is equal to _______ in the Hardy-Weinberg eqn
q2
Taking the square root of _______ and subtracting it from 1 yields _______
q2 p (the number of wild-type alleles in the population)
Plugging p and q back into the equation gives the frequencies of the _______ and_______ genotypes (genotypes that we would not be distinguishable based on phenotype alone)
AA
Aa
In order for the Hardy Weinberg principle to be upheld, a number of assumptions are made (4)
- The population is large and mating is random
- Allele frequencies remain constant over time (meaning no new mutations)
- All individuals are equally capable of mating and passing on their genes (certain alleles are not selected for)
- There has been no significant immigration of individuals with significantly different allele frequencies
_______ is the main determinant in whether or not a mutant gene is passed onto future generations in order to become stable in a population
Fitness
Fitness
describes the number of offspring of persons affected by a mutation survive to reproductive age
For an autosomal dominant disease: µ =
0.5 F (1-f)
For an autosomal recessive disease: µ =
F(1-f)
For an X-linked recessive disease: µ =
0.333 F (1-f)
A mutant allele that is as likely to represented in the next generation as the wild-type allele has a fitness of
1 (f=1)
a mutant allele that causes death or sterility has a fitness of
0 (f=0)
Autosomal recessive mutations
generally have little short-term effect on allele frequencies in populations. The number of expressed mutations is generally much lower than the frequency of heterozygotes. Most of the recessive alleles are hidden in heterozygotes and are unaffected by selection.
_______ and _______ occur at approximately the same rate as recessive mutations, but perturb the allele frequency of a population to a greater extent because they are expressed to a greater degree and are, therefore, selected for at a higher frequency.
X-linked
autosomal dominant mutations
The effect of a mutation in a population is amplified when _______ exists.
consanguinity
Consanguinity
increases the frequency of mating between carriers of an autosomal recessive disorder.
This allows for a higher frequency of offspring homozygous for the recessive mutant allele.
As a result, rare recessive disorders are more frequent in these populations
Other factors that cause the frequency of mutated alleles to shift from what would be predicted by the Hardy-Weinberg principle are
population stratification, assortative mating, genetic drift and migration
How do physicians contribute to the increase in prevalence of genetic illnesses?
decreasing selection against mutant genes that would otherwise have a deleterious effect.
- inc the fitness of mutant alleles by improving their health & reproductive capacity
- mutant alleles able to make it to reproductive age and pass on their mutant alleles onto future generations
