What is a population
Interbreeding group of individuals that belong to the same species and live within a restricted geographical area
is the frequency of an allele in a population the same as the ratio in a single cross
no, not often
how did population genetics introduce a shift from mendelian genetics?
it shifted from individual to population level thinking
What were Darwin’s conditions for evolution to occur by natural selection
- individuals with a species may vary
- some of the variation has to be able to be passed down to offspring (being heritable)
- survival and reproduction is not random but its an association between fitness and phenotypic variation
In what conditions which evolution by natural selection not occur
- no variation present
- variation is not heritable
- variation is heritable but it has no association to fitness
What happens to genetic variation in the absence of evolution?
variation will remain unchanged over time
What is the null hypothesis for evolution?
if evolution is change in allele frequencies over time, then the null hypothesis should be no change in allele frequencies over time
Hardy Weinburg established the conditions for an environment where evolution wouldn’t occur.
- no mutations (no new alleles arising in the population)
- no gene flow (alleles aren’t added to the population)
- infinitly big population size (this way the effect of random processes that could change allele frequencies are eliminated)
- Natural selection does not affect the alleles considered, all diploid individuals have the same fitness, same probability to breed, and same mating/fertilizing ability.
- Random mating
If these conditions are met then population allele frequencies do not change
In the HWE equation p+q=1, what does p stand for, what does q stand for, and why is 1 important
p = the frequency of the dominant allele
q= the frequency of the recessive allele
1 = both alleles add up to 100%
T or F, even if a population is not in HWE, one round of random mating with the other conditions met can return the population to equilibrium
T
In the HWE formula p^2 + 2pq + q^2 what does each term mean
p^2 = the frequency of the AA genotype
2pq = the frequency of the Aa genotype
q^2 = the frequency of the aa genotype
T or F, even if a population is not in HWE, this doesn’t prove that it is evolving - we need a sustained change in frequencies to be able to predict this.
T
In sickle cell disease how do the individual genotypes translate to phenotypes?
homozygous for Hs means correlates with severe sickle cell anemia.
Heterozygous correlates with mild SCA (codominant)
How is SCA relate to malaria in a population?
people with SCA have better protection against SCA due to the shape of the cells. This means that the heterozygous genotype best suits both condidtions of SCA and malaria.
What are the steps to testing if a population is in HWE
- calculate allele frequencies from p+q=1
- use this information to calculate expected genotype ratios
- calculate the number of indivdiuals this would correlate with
- compare the observed to the expected
Is SCA and malaria an example of Natural selection?
yes
