Mendelian Genetics in Populations II: Migration, Genetic Drift, and Nonrandom Mating
I. Motivation
What happens when we depart from HW assumptions?
Pattern of genetic diversity, fitness consequences.
II. Migration
Movement of genotypes between populations
Can rapidly alter allele frequencies
Homogenizing effect
Example: Silene dioica
Migration and Selection: Can lead to equilibrium, Banded water snake example
III. Drift and Consequences for Genetic Diversity
Reduces genetic diversity within populations, increases genetic differences Between pops.
Colonization can be a bottlenecking process, leading to drift
Silvereye and Drosophila example
Effective population number/size: determined by sex ratio, variation in number of individuals
The size of the population that would give rise to the observed loss of heterozygosity each
generation, or increase of variation between populations each generation.
Wahlund effect and consequences of fragmentation,
Fst is a measure of the degree to which populations are differentiated:
Probability of Identity by Descent due to population differentiation.
Collared lizard example
Drift and the molecular clock
Selection versus Drift at the Molecular level
IV. Inbreeding (A form of Non Random Mating)
Mating between relatives
Drift can lead to inbreeding
Drift and inbreeding can have the same consequences
Leviticus 18 example
Contemporary patterns of inbreeding within human populations
Inbreeding and outbreeding in other organisms
Fitness consequences of inbreeding: inbreeding depression (the loss of vigor expressed in inbred
progeny relative to non inbred progeny)
Measuring the degree of inbreeding: F: probability that the two alleles in an individual are
Identical By Descent
Calculating F
Consequences of inbreeding/Drift at the population level
Prairie Chicken example, Lakeside Daisy example, Clarkia example, Fritallary example
Key Concepts: Drift, how you get drift, inbreeding, what promotes inbreeding, consequences of
inbreeding and drift at the molecular, individual and population level