Population Genetics Flashcards
What is population genetics?
The study of the distribution of genetic variation in a population.
gene pool
collection of all the alleles at a particular locus in a population
Key assumptions for Hardy-Weinburg equilibrium
- No new mutations
- No evolutionary selection
- No migration
- Infinitely large population
- Matings are random
How to calculate the carrier frequency
Calculate 2pq
Problems with random mating
- Stratification
- Assortative mating
- Consanguinity
Maple Syrup Urine Disease
- consanguinity
- caused by founder effect: original founder carried allele
- genetic isolates
What is evolution?
The process whereby the fittest alleles are selected
Fitness (f)
A measure of the number of offspring of affected persons who survive to reproductive age
f=0
- causes death
- no fitness
f between 0 and 1
-deleterious
f=1
just as likely to be represented in next generation as wild type allele
Coefficient of selection
- the proportion of mutant alleles that are not passed on and are lost because of selection
- s = 1 - f
If s = 1, it means….
it is a genetic lethal
Why is selection on autosomal recessive disorders slow/ineffective?
- Most individuals with recessive allele are heterozygous
- Heterozygotes have the same phenotype (and fitness) as homozygous dominant individuals
- Selection can only act on expressed traits.
Why does selection on autosomal dominant disorders happen much more quickly?
- Exposed to selection
- Heterozygotes have the same phenotype as homozygous dominant individuals, so they will also be selected against
- If zero fitness, new cases have to come from de novo mutation
Genetic drift
changes to allele frequencies due to random chance/sampling error
Population bottlenecks
Occur when many member of a group die, and few remain to re-start the population
Fixed allele
the only allele for a single gene in the population
Lost allele
No longer found in the population
Loss of heterozygosity
As we get drift towards loss/fixation, heterozygote frequency decreases
Does heterozygosity increase or decrease with every generation with a fixed population?
decrease
Characteristics of an ideal population
- males = females
- All animals can reproduce
- All animals equally likely to produce offspring
- Mating is random
- Population size is constant
- No migration/mutation/selection
Effective population size equation
Ne = 4(Nm)(Nf)/(Nm + Nf)
