Chapter 20 - Population Genetics

population genetics

extension of Mendel’s basic principles

too to learn bio function, evolutionary mechanisms, and human history

population

group of interbreeding individuals of a single species living in the same time and place 

gene pool

total of all alleles carried in all members of a population

sample

number of individuals used to make inferences about the entire population

phenotypic frequency

proportion of individuals that have particular phenotype

genotypic frequency

proportion of individuals in a population that carry a particular genotype

allelic frequency 

proportion of gene copies in a population of a given allele type 

hardy weinberg equilibrium

• correlates allelic and genotype frequencies

  • developed independently in 1908 by hardy and weinberg

• allele and genotype frequencies will not change unless one of its conditions is violated

1. population has an infinite number of individuals

2. individuals mate at random

3. no new mutations

4. no migration into or out of population

5. genotypes have no affect on the ability to survive and transmit alleles to the next generation

five assumptions of hardy weinberg

1. allele frequencies are the same in adults and gametes

2. allele frequencies can be used to predict genetype frequencies of the next generation

sexually reproducing diploid organisms with equal segregation and random mating have two important outcomes - what are they?

p2 + 2pq + q2 = 1

HWE equation 

one

in a population not in HWE, ____ generation of random mating can reshuffle alleles into equilibrium

short term

is HWE better for short term or long term population tracking?

monte carlo simulations

use a computer program to model possible outcomes of randomly chosen matings over a designated number of generations

• starting population has a defined number

• genotypes of offspring are based on probabilities

• offspring and parental population sizes are equal 

• parental discarded and offspring become new parents 

genetic drift 

changes is allele frequencies as a consequence of randomness in inheritance due to sampling error from one generation to the next 

fixation

when only one allele in a population has survived and all individuals are homozygous for that allele

• no further changes can occur

• allele frequency changes are small (unless it’s over many generations than maybe larger)

founder effects

a few individuals separate from the population and start their own thing

population bottlenecks

large proportion of individuals die from environmental disturbances

mutation

variant DNA sequence in individual genome that was not present in either parent 

• deleterious - delete important functions

• beneficial - selective advantage

• neutral - no benefit or harm

molecular clock

• mutations accumulate in populations at constant rates

• DNA differences between organisms can be used to estimate how long ago they shared a common ancestor

fitness

individual’s relative ability to survive and transmit its genes to the next generation

• cannot be measured in individuals within a population

• can be measured in all individuals with same genotype in a population

• viability and reproductive success

natural selection 

process that eliminates individuals whose fitness is lower 

• higher fitness become parents

• occurs in all natural populations

• results in decreased genetic diversity