Ch07
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List the Hardy-Weinberg assumptions
(1) No Natural Selection (2) Random mating (3) No mutation (4) No migration (5) Infinitely large population
List the Hardy-Weinberg conclusion
(1) Allele frequencies do not change through time (2) Given random mating, equilibrium genotype frequencies can be predicted (3) Equilibrium frequencies will be reached in one generation
Why is it that in the HW model allele frequencies are at a neural equilibrium, while genotype frequencies are at a stable equilibrium?
Because p & q can take any value Because there is an equilibrium genotype frequency for every p value
Why dominant alleles would not replace recessive alleles in a population over time?
there is a BIG difference between allele Expression & Transmission
Define selection coefficient (s)
selection strength for or against a particular phenotype or genotype
What happens when s is larger
NS would be stronger, alleles frequencies change faster, & favored allele reach fixation faster
Both fitness & selection coefficient are context specific, so they are…
expected to vary among populations & time
Define Frequency-independent selection
Genotype fitness is NOT influenced by its frequency in population
Define Directional selection
Selection where one allele is consistently favored over other *CDA1A2>DA1>RA1
Define Overdominance
when heterozygote has the highest fitness. stable equilibrium ex. Sickle-cell anemia
Define Underdominance
where heterozygote has the lowest fitness. Has 2 possible fixation. unstable equilibrium
Define Frequency-dependent selection
Genotype fitness is influenced by its frequency in the population
Explain Positive frequency-dependent selection
as frequency increases, fitness increases. one allele will eventually be fixed & the other will be lost depending on the initial allele frequencies ex. flat snail
Explain Negative frequency-dependent selection
as frequency decreases, fitness increases. When the frequency of one type becomes greater than the other, frequency-dependent selection brings population back to a 50–50 split. This causes a fluctuation between two phenotype over time ex. fish bite
Explain Mutation–selection balance
At equilibrium, the rate of mutation from favored A1 alleles to disfavored A2 alleles (μ) is balanced by selection against disfavored A2 alleles (s). This does not eliminate disfavored A2 alleles Ex. Familial adenomatous polyposis
Explain Effects of Non-random mating
Does not change allele frequencies, but changes genotype frequencies from what is expected under the HW model. It disrupts HW equilibrium
Define Assortative mating
individuals tend to mate with those of the same genotype or phenotype. Frequency of heterozygous individuals decrease & those of homozygotes increase
Define Disassortative mating
individuals tend to mate with those of different genotypes or phenotypes. Frequency of heterozygous individuals increases & those of homozygotes decrease
What effects does Inbreeding have on allele frequencies?
In the absence of any other evolutionary forces allele frequencies remain the same
Define Inbreeding depression
occurs when the offspring from matings between genetic relatives have reduced fitnesses
What effects does Migration have on allele frequencies?
Excluding all other evolutionary forces, migrations tend to homogenize allele frequencies