Melanie Pritchard; Week 4 MED1011; Biochemistry
Sum of all alleles is the gene pool. Sum of all allele frequencies at a locus = 1.
- Frequency = p = number of all copies of an allele in a population/sum of all alleles
- Genotype frequency = number of individuals with a particular genotype in a population/total number of individuals in a population
If allele frequency of A is 0.6 (p) and a is 0.4 (q); prediction of AA frequency = 0.6 x 0.3 = 0.36 (psquared); Aa = 0.4 x 0.6 x 2 = 0.48 (2pq); aa = 0.4 x 0.4 = 0.16 (qsquared); total equals 1
Hardy-Weinberg law- in large randomly mating populations allele frequencies do not change over time in the absence of migration, mutation or selection
Hardy-Weinberg equilibrium is a model situation in which allele frequencies do not change. It is useful for predicting genotype frequencies from allele frequencies, model describes conditions if there were no evolution, frequency deviations should prompt a search for factors that cause the deviation (heterozygote advantage or assortative mating which is attraction to similar).
Carrier frequency can be estimated: disease incidence = q squared, gene frequency is q, carrier frequency is 2pq (p + q has to equal 1)
Factors disrupting Hardy-Weinberg are mutation, migration, positive or negative selection, genetic drift, non-random mating. If large variation from HW is found there is likely to be another mechanism involved. Gene flow is a result of the migration of individuals and movements of gametes between populations. Positive or negative selection can occur for alleles due to natural selection pressures.
If population is bottlenecked, genetic drift can reduce genetic variation. It also affects small populations that colonise a new region. Founder effect is equivalent to a bottleneck.
Several populations have higher rare autosomal recessive disease incidence, founder effect with geographical/social/religious isolation
Consanginuity is inbreeding.