ANSC 446: Population Genetics - Exam 3

Bottleneck

periods during which only a few individuals survive to continue the existence of the population

Founder Effect

loss of genetic variation when a new population is established by a small number of individuals from a larger founding population. May lead to low genetic variation or, by chance, to unusually high or low frequencies for some alleles

Genetic drift

chance allele frequency changes due to finite population sizes

Absorbing states

The levels at which an allele becomes either lost in the population, or fixed in the population (i.e., where allele frequency becomes 0 or 1), after which allele frequency cannot be changed by drift in subsequent generations (barring mutation, migration, etc)

Mutation

change to the nucleotide sequence of the genetic material

Frameshift mutant

indel that changes the reading frame of subsequent codons in a transcript

Gene conversion

part of the nucleotide sequence from one allele is replaced by the homologous nucleotide sequence of another allele (without the sequence of the first allele replacing that of the second)

Mutation

selection balance

Mutation load

reduction in fitness due to deleterious mutants not yet removed by selection

Two major components of genetic load

1) Mutation load due to deleterious mutants not yet removed by selection

2) Homozygote genotypes at loci subject to overdominant selection

Orthologous genes

separated by a speciation event (eg, most single copy genes in humans will also be found as a single copy gene in the chimpanzee)

Paralogous genes

separated by a duplication event (eg, the genes encoding myoglobin and hemoglobin descend from duplication of an ancestral gene)

Monoecious

plants with male and female reproductive organs on the same individual

Infinite allele model

assumes that every new mutation does not match any previous mutation (and is thus a novel allele). Model is used to examine the balance between the creation of new alleles by mutation and the elimination of alleles by drift

Relative rate rest

determines if different lineages are evolving at the same pace

Molecular clock

Loci for which there is a constant rate of substitution, equal to the mutation rate, and constant over time; and can thus be used to estimate divergence times between taxa

Gene flow

the transfer of alleles of genes from one population to another

Continent

island model of migration

General model of migration

A population is divided into k subpopulations, with gene flow possible in all directions for all subpopulations. Allele frequencies shift towards a common frequency

Wahlund effect

subpopulation structure leads to reduction in overall heterozygosity, even if the subpopulations themselves are in Hardy

Admixture

the proportion of gene flow from an outside population

Metapopulation

subpopulations in discrete habitat patches, that turnover with extinction and recolonization from other patches. The newly colonized patches may display the results of founder effects

Cline

a directional change in allele frequencies across (geographic) space or between subpopulations (or between species), potentially due to selection or substructure. May be stable or transient

F ST

"Fixation index," genetic differentiation over subpopulations. Measures the degree of genetic variation that is due to the differences between two (or more) subpopulations. Never negative. Zero if subpopulations have similar allele frequencies; increasingly positive as the populations become more divergent

F IS

Deviation from Hardy

F IT

Deviation from Hardy

Name a type of transposable element present in the human genome

short interspersed nuclear elements (SINEs) such as Alu sequences

What are three things that zoos could do to minimize the loss of genetic diversity in the captive population?

1. Increase population size (doubling cuts rate of loss of diversity in half)

2. Equalize the mating success of all individuals (equalize the contribution of each founder), increases the Ne to twice the census size

3. Store gametes and/or cell lines in liquid nitrogen, use these to restore any genetic diversity lost, using advanced reproductive technology

An example of a population that has undergone a bottleneck or a founder effect

Florida Panther, and humans on Tristan da Cunha