LIFESCI 1 Lecture Notes - Lecture 6: Allele Frequency, Genotype Frequency, Genetic Drift
From Last Time
• Genetic Drift changes the allele frequencies over time
• But genotype frequencies conform to HWE. Why? Because of random mating and
roughly HW genotype frequencies but because of genetic drift allele frequencies will
alter
• Inbreeding itself does not change allele frequencies
-changes genotype frequencies
Leads to more homozygotes than HWE
- Because inbreeding is not random mating
• Drift and inbreeding each occur when an individual has a higher chance of inheriting two
copies of the same allele from a single ancestor because of violations of the HWE
Inbreeding and Inbreeding Depression
• Inbreeding → recessive alleles expressed; deleterious recessives
• Natural selection can act on them
• NS can purge genes with large negative effects from population
• Ex. Hutterites; started with 12 families; now most fecund
Mountain Gorilla Genomes
• Far fewer loss-of-function allele than we’d expect
• Inbreeding → expression of deleterious alleles
• NS can act on deleterious recessives once theyre expressed but not if they aren’t
• NS purged LOF alleles from gorilla population
• NS changes allele frequencies
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Document Summary
From last time: genetic drift changes the allele frequencies over time, but genotype frequencies conform to hwe. Because of random mating and roughly hw genotype frequencies but because of genetic drift allele frequencies will alter. Because inbreeding is not random mating: drift and inbreeding each occur when an individual has a higher chance of inheriting two copies of the same allele from a single ancestor because of violations of the hwe. Inbreeding recessive alleles expressed; deleterious recessives: natural selection can act on them, ns can purge genes with large negative effects from population, ex. Hutterites; started with 12 families; now most fecund. Mountain gorilla genomes: far fewer loss-of-function allele than we"d expect. Inbreeding expression of deleterious alleles: ns can act on deleterious recessives once theyre expressed but not if they aren"t, ns purged lof alleles from gorilla population, ns changes allele frequencies. Two other mechanisms: gene flow emigration/immigration. Can constrain a population from reaching naturally selected optimum.
