Population Genetics - Biochemistry

Overview
- Forces responsible for genetic variation
  - mutation
    
    de novo mutation rates constant among populations
    
    intrinsic error rate in DNA polymerase
  - founder effect
    
    if one member of a small community carries a triat, as the population expands there will be a higher frequency of that trait in the new community than there is in the general population
    
    Ex.) Pennsylvania Amish and Ellis-van Creveld syndrome
  - genetic drift
    
    a dramatic change in allele frequency based on chance
    
    small populations are more vulnerable to genetic drift
  - natural selection
    
    ↑ in allelic frequency that ↑ species fitness
    
    ↓ in allelic frequency that ↓ species fitness
    
    some genes ↑ species fitness as heterozygote but ↓ species fitness as a homozygote
    
    ex.) sickle cell trait lowers malarial infections, while sickle cell anemia is detrimental
  - bottleneck
    
    Even when fitness is equal for all phenotypes, a population bottleneck can result in disrupted allelic frequencies or loss of a genotype all together by chance
  - gene flow
    
    transfer of alleles from one population to another
- Hardy-Weinberg equilibrium
  - states that genotype and allele frequencies remain constant through generations
  - disease prevalence equation
    
    p²+ 2pq + q² = 1
    
    where p = frequency of allele A
    
    where q = frequency of allele B
    
    p² = frequency of homozygous individuals for allele A
    
    q² = frequency of homozygous individuals for allele B
    
    2pq = frequency of heterozygotes
  - requirements for validity
    
    large population
    
    random mating
  - the genotypic frequencies of the population will remain stable from generation to generation
  - assumptions
    
    no mutation
    
    no selection for any of the genotypes at the locus
    
    no migration
  - other notes
    
    prevalence of an X-linked recessive disease in males = q
    
    prevalence of an X-linked recessive disease in females = q²
    
    possible to assume in most cases that p = 1 as the wild-type allele is approximately 1

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T