Lecture 34 Flashcards
What is Hardy Weinberg equilibrium?
-genotypes are in the proportions if p= f(A) allele q = f(a) allele
p2+2pq+q2=1
p2= f(AA)
2pq=f(Aa)
q2=f(aa)
-remaining constant across generations
This equilibrium acts as a reference point for all population genetics studies
However constancy of allele frequencies does not necessarily
indicate a Hardy-Weinberg equilibrium
-when you have hardy weinberg equilibrium you can maintain the genotypic proportions from generation to generation
What are the 5 assumptions of the Hardy-Weinberg law?
- Random mating=equally likely to mate with everyone, no preference allowed
- No migration (no gene flow)= no new alleles brought in
- No selection acting= once a partner equally likely to have the same no. of offspring, none is more fit than the other
- No mutation=no new alleles, or equally in both direction
- Infinite population size = large enough to prevent sampling errors and random effects
What does H-W refer to?
-genotypic frequencies remaining constant in the proportion and as a consequence constant allele frequencies result
How do you know if population is in H-W equilibrium?
.
What are selective agents?
-Factors in the environment which discriminate between phenotypes and or genotypes
eg.,
climate pollution predators disease insecticide antibiotics…….
Fitness can change in different environments
What is w and s?
w-fitness and s is the selection against
- one phenotype always has fitness 1 and anotehr has less
- s = if w=0 then s=1
what happens in a malarial region?
-in non malarial region HbA frequency tends towards monomorphism
malarial region = constant allele frequencies= stable or balanced polymorphism = but not HW because there is selection!
conclusion from sickle cell study: selection may alter allele frequencies or keep them constant
so sometimes even when have stable allele frequencies= doesn’t have to be HW equilibrium
