Population and evolution genetics Flashcards
week 8
How does natural selection drive evolution?
1- majority of individuals show common phenotypes and will follow a normal distribution.
2- reflects ability for individuals to pass on genes to the next generation
if dominant traits are usually good, why don’t these alleles take over the population?
selection occurs at the level of phenotype, not genotype
What is the Hardy-Weinberg equation? (what does each part mean)
p^2 + 2pq + q^2 = 1
P^2= homozygou dominant
2pq= heterozygous
Q^2 = homozygous recessive
for two alleles at a single locus , the genotype freq=
expansion of binomial expression
(p+q)^2 = (p^2 + 2pq + q^2) = 1
For three alleles at a single locus, the genotype freq =
trionomial expression
What does a H-W equilibrium mean for a population?
Allele and genotype frequency will remain constant from generation to generation in a population
What is needed to reach H-W equlibrium?
Large breeding population
Random mating
No mutation of alleles
No migration
No selection
How is H-W equilibrium proved mathematically?
Chi square test= observed value is close to expected value
What is selective advantage?
deleterious allele maintained if heterozygote carrier is more reproductively fit than homozygous.
What are the four exceptions of H-W equilibrium?
Non-random mating – much mating is selective based on phenotypic traits
Unequal survival – driving force of NS, selective disadvantage and selective advantage
Population subdivisions panmictic (anyone can mate with anyone) is unrealistic, allele can be equal in subpopulations but not overall
Migration: allele freq differ between population and immigration is continuous = constant disruption
How do subdivisions affect a population?
inhomogenous (whole mass does not look the same)
what is the founder effect?
small-sub population becomes isolated = decreased genetic diversity = deleterious alleles reach higher frequencies
Bottle neck effect
sharp reduction in population due to natural disaster = initially lower genetic diversity –> slowly increases over time due to random mutations
what is random genetic drift and what is the impact of it? (1.5 marks)
in small numbers, Mendelian segregation = random drifting of population allele freq = alleles lost by breeding patterns
Define population genetics
Genetic composition of a biological population
changes in genetic composition from various factors
