Population Genetics Flashcards
What do haploid gametes show allele frequency or genotype frequency?
Allele frequency
What do diploid gametes show allele frequency or genotype frequency?
Genotypic frequency
What is population genetics theory?
The frequencies of alleles and genotypes in a population will remain constant unless acted upon by non-mendelian processes
(equilibrium = no evolution)
How did Theodosius Dobzhansky define evolution?
“a change in the frequency of an allele within a gene pool”
What does a mendelian inheritance patterns allow us to predict?
Expected frequencies of alleles
When do frequencies of alleles remain constant?
in offsprings
What does p stand for in the hardy-weinberg equilibrium?
the frequency of one allele in the
population (usually the dominant allele)
What does q stand for in the hardy-weinberg equilibrium?
the frequency of one allele in the
population (usually the recessive allele)
What is hardy-weinberg equilibrium equation?
p^2 + 2pq + q^2 = 1
p + q = 1
What does p^2 stand for in the hardy-weinberg equilibrium?
Proportion of population that is homozygous for the first allele
What does 2pq stand for in the hardy-weinberg equilibrium?
Proportion of population that is heterozygous
What does q^2 stand for in the hardy-weinberg equilibrium?
Proportion of population that is homozygous for the second allele
When does the hardy-weinberg equilibrium apply?
- Organisms are diploid, sexual and have discrete generations
- Allele frequencies are the same in each sex
- Mendelian segregation occurs
- Mating occurs at random
- Population size is large so no genetic drift
- No gene flow (immigration/ emigration)
- No mutation
- No selection
Why must mating occur at random when using the HWE?
Non-random mating does not change allele frequencies, but rather changes how the alleles are distributed into diploid genotypes
What is assortative mating?
- Race and geographical proximity
- Mating is generally random with respect to genotypes
What is positive assortative mating?
People that looks the same
What is negative assortative mating?
People that looks the different
Why must the population be large so no genetic drift when using the HWE?
- Because genetic drift affects smaller populations more than larger populations.
- Genetic drift reduces genetic variation.
What is genetic drift?
Allele frequency change due to chance as a result of sampling error.
Why must there be no migration or gene flow when using the HWE?
- Migration transfers individuals amongst populations.
- Gene flow transfers alleles amongst populations.
- Can either ↑ or ↓ genetic variation.
Why must there be no mutations when using the HWE?
- Mutations increase genetic variation.
- Some mutations create dominant alleles, some create recessive or co-dominant alleles.
- Mutations may be harmful, neutral, or favourable.
- Effect depends on the environment
Why must there be no selection when using the HWE?
- biases which genotypes are transmitted to the next generation.
- can either ↑ or ↓ genetic variation depending on the type of selection.
- can operate in many different ways.
What is linkage disequilibrium?
Deviations from the expectations of independent segregation and Hardy-Weinberg equilibrium caused either by physical linkage or population demography
How do you workout the HWE and linkage probability?
D = pAB x pab - pAb x pAB
