Lecture 30 Flashcards
what are the conditions required for hardy weinberg equilibrium?
- very large population
- random mating
- no selection for or against particular genotypes
- no migration in or out of the population
how many alleles for every person?
2
what are the two hardy weinberg equations?
p^2 + 2pq + q^2 = 1
p + q = 1
how do the hardy weinberg rules change for X-linked recessive diseases?
they don’t change for females since they have two X chromosomes so the alleles are still squared. For men however, there is no need to square for men since there is only one X chromosome, there are no true carriers: p and q are direct measures of affected and unaffected (no carriers).
- disease incidence in males directly estimates q
how do the hardy weinberg rules change for autosomal dominant diseases?
carriers are rare because they get selected against since they have the disease. homozygous dominant are even more rare. P is going to be very high, close to 1 and incidence of disease (affected/carriers) is going to be approximated to 2q.
what does q always represent?
the mutant allele
when is a population not in equilibrium?
when the frequency of heterozygotes observed is not that predicted from the frequency of homozygotes.
what size does the population need to be in order to experience close to equilibrium conditions?
over a thousand
what is genetic drift?
it is the random shifting of genotypes within a population due to mating. It is similar to natural selection only there is no selection for a particular advantageous trait, it is completely random and usually happens more in smaller populations.
what are some things that can affect random mating?
geographical barriers, religious barriers, and assortive mating (choosing a mate based on shared or preffered traits)
what does selection usually result in within a population?
it distorts hardy weinberg because it favors heterozygotes. Consider the resistance to malaria that sickle cell carriers have, or the resistance to cholera that cystic fibrosis carriers have.
What is the founder effect?
this is the loss of genetic variability due to a new population being established by a relatively small group of individuals with obviously limited genotypes. Consider Huntingtons disease in that tiny fishing village in venezuela with 40% affected.
