CHAPTER 20 Flashcards
Compare mendelian genetics and population genetics
- Generations and relationship among individual: M - known, P - generally unknown
- Number of analyzed alleles: M - usually two, P - Highly variable
- Forces influencing individuals/populations: M - known and controlled, P- unknown and inferred
- Mode of reproduction: M - Known, P - from known to unknown depending on organism
Def: Population
a group of interbreeding organisms
Def: Gene pool
The collection of genes and alleles found in the members of a population
Def: Population genetics
The study of allele frequencies and genotype frequencies within and between population
Def: Evolution
Changes of allele frequency and genotype frequency over time
Hardy-Weinberg equilibrium
Populations with observed genotype frequencies at individual loci not different from expected based on random mating
HWE equation
p^2 + 2pq + q^2 = 1
Assumptions of Hardy-Weinberg equilibrium
- Population size is infinite
- Random mating occurs in the population, allowing genotype frequencies to be predicted by allele frequencies
- Natural selection does not operate
- Migration does not introduce new alleles
- Mutation does not introduce new alleles
- Genetic drift does not occur
Predictions of HWE
- Allele frequencies remain stable over time
- Allele distribution into genotypes is predictable
- Stable equilibrium frequencies of alleles and genotypes are maintained
- Evolutionary and nonrandom mating effects are predictable
Calculating expected genotype and allele frequencies in HWE for more than two alleles
ALLELE FREQUENCIES
p + q + r = 1
GENOTYPE FREQUENCIES
p^2 + 2pq +2pr + q^2 + 2qr + r^2 = 1
How to determine autosomal allele frequencies from genotype frequencies in populations
- The gene-counting method: co-dominant alleles
- The square root method
- Dominant-recessive alleles, assumes HW equilibrium
Major forces that change allele frequencies in a population over time
SOURCES OF GENETIC VARIABILITY
- Mutation
- Mode of reproduction
- Gene flow
Lead to population-environmental interactions
- Natural Section
- Genetic drift
ALL LEAD TO EVOLUTION
Directional artificial selection favoring the AdhF allele in experimental Drosophila population
- In high frequency AdhF in high ethanol environment
- Relatively stable frequencies in zero-ethanol environment
Balanced polymorphism
Alleles reach stable equilibrium frequencies that are maintained in a steady state balancing the selective pressures favoring the maintenance of a mutant allele when it occurs in a heterozygote but acting against it when it occurs in a homozygous genotype
Allele frequencies in balanced polymorphsims
- t: fitness disadvantage of cc vs Cc
- s: fitness disadvantage of CC vs Cc
- pe (allele frequency C) = t/(s+t)
- qe (allele frequency c) = s/(s+t)
Forward Mutation rate
u
The rate of creating new alleles
Reverse mutation rate
v
rate of mutation to original allele
Results of gene flow
- Introduce novel alleles
- Increase frequency pf existing alleles
- Remove/reduce existing alleles
- Create admixed population
Genetic drift
chance fluctuations of allele frequencies due to sampling bias
Inbreeding
Mating between related individuals - increases homozygous genotypes
Biological species concept
a group of organisms capable of interbreeding with each other but isolated from other species
Allopatric speciation
populations diverge due to physical barrier and thus new species develop in separate geographic locations
Sympatric speciation
populations share a territory but are isolated by genetic, behavioral, seasonal, or ecosystem-based mechanisms that prevent gene flow
Hybrid speciation
formation of new species due to hybridization between existing species
Prezygotic mechanism of reproductive isolation
- Behavioral
- Gametic
- Geographical
- Habitat
- Mechanical
- Temporal
Postzygotic mechanisms of reproductive isolation
- hybrid breakdown: deceased fitness of F1 progeny
- Hybrid inviability: fails to survive gestation
- Hybrid sterility
Mutation-selection balance
- equilibrium frequence of recessive allele qE = sqrt(u/s)
u = mutation rate
s = selection co-efficient against mutant allele
Fonder effect
The reduced genetic diversity when a population is descended from a small number of colonizing ancestors
Genetic bottleneck
event limits generation size or genetic variation, large genetic drift effect
