BIOCH Y1 S1: Population Genetics Flashcards
population genetics
- study of genetic variation within population
- changes in allele frequency over time
population genomics
- applications of genomic technologies e.g. genotyping/DNA sequencing
- understand how genes contribute to our HWB
why is pop genetics important?
- genetic variants that contribute to a disease may vary across populations
- prevalence of genetic disorders
- confirm diagnoses/provide genetic counselling
- informs drug testing e.g. need to use samples from diff populations which have diff alleles = diff responses to drugs
gene pool
- sum of all alleles
allele frequency
- proportion of one allele in the gene pool (all ALLELES, not phenotypes)
are allele frequency and phenotype frequency always the same in diff populations?
NO
- allele frequency can be the same however they may be in different combinations of phenotypes
formulas for 3 genotype frequencies
freq(A) = p and freq(a) = q
- f(AA) = p^2
- f(Aa) = 2pq
- f(aa) = q^2
Hardy-Weinberg law
- in large, randomly mating populations, allele frequencies do not change
(in the absence of migration, mutation or selection)
Hardy-weinberg equilibrium
- model situation in which allele frequencies don’t change
- little difference between observed genotype frequency and expected genotype frequency
hardy-weinberg equation
p^2 + 2pq + q^2 = 1
why is the hardy-weinberg law useful?
- predicting genotypes from allele frequencies
- patterns of deviation from the model would help identify if evolution has occurred
- genotype frequencies that deviate should prompt a search for factors that cause the deviation (e.g. selective advantage)
- estimate mutation rates
genotype expected value formula
- genotype frequency proportion x no. of individuals in population
how does sickle-cell anaemia lead to heterozygote advantage?
- heterozygotes are relatively resistant to malaria parasite b/c their RBC are sickled and can’t be attacked
- selective advantage > proportion of heterozygotes will increase in population
factors that disrupt hardy-weinberg equilibrium
- mutation
- migration
- non-random mating
- positive or negative selection
how does mutation disrupt the hardy-weinberg equilibrium
- only minor because natural mutation rate is very low
- larger deviations could suggest mutations due to other factors
how does migration disrupt the hardy-weinberg equilibrium
- results in gene flow
- new alleles can be added > change in allele frequency
how does non-random mating disrupt the hardy-weinberg equilibrium
- consanguinity/inbreeding leads to an increase in homozygotes
- outbreeding leads to increased heterozygotes
how does positive or negative selection disrupt the hardy-weinberg equilibrium
- more/less biological fitness = more likely to survive/die and have offspring = more/less allele frequency
founder effect (genetic drift)
- a few individuals from a population start a new population w/ a diff allele frequency than OG population = smaller gene pool/reduced variation
single nucleotide polymorphism (SNP) + effects
- difference in one nucleotide b/n members of a species
- must occur in >1% of the population
- (if <1% then called single nucleotide variance)
- 50% are in introns, 25% silent mutation, 25% missense mutation
human genome project
- sequenced the entire human genome
- used multiple people to retain confidentiality/privacy
use the hardy-weinberg theory to calculate the carrier frequency of an autosomal recessive disorder, given that the disease incidence in a population is 1/10,000
- disease incidence (aa) = 1/10,000 = q^2
- allele frequency (q - recessive) = root(1/10,000) = 1/100
- since p + q = 1, then p = 99/100
- carrier frequency = 2pq = 1/50 = 0.02
