Unit 2

Evolution

change in the genetic composition (allele frequencies) of a population across successive generations

Genetic Drift

random changes in allele frequency by chance in finite populations

due to random sampling of gametes

particularly important for small populations

Wright-Fisher Model

probability of exactly i A alleles in next generation is binomial distribution

assumes two alleles

assumes non-overlapping generations

Effective Population Size

a correction for the fact that many population genetics models assume an idealized population

Bottleneck

large population is reduced then re-expands

Founder Effect

genetic effect on a population started by a small group of individuals

alleles in the group become the alleles of the population

Natural Theory of Molecular Evolution

at the molecular level, most evolutionary changes and most of the variation within and between species is not caused by natural selection but by random drift of neutral alleles that are neutral

Selection

differing reproduction rates of different genotypes

Absolute Fitness Coefficients

the proportional abundance of a genotype over one generation

can be observed

often capital Ws

Relative Fitness Coefficients

the other genotype’s fitness coefficients are relative to the reference genotype

what is cared about in terms of change in allele frequencies

often lowercase ws

Selection Coefficient (s)

describes the degree of selection against the aa genotype

Dominance Coefficient (h)

describes the degree of dominance

Directional/Positive/Darwinian Selection

selection favors the adaptive allele

used to describe selection when when phenotypic variation is changing

Stabilizing/Negative/Purifying Selection

selection disfavors a maladaptive or deleterious allele

used to describe selection when phenotypic variation is not really changing

Balancing Selection

selection favors diversity

Disruptive/Diversifying Selection

selection disfavors the intermediate or mean; selection favors extremes

not stable and leads to niche partitioning and speciation

Mutation

change in the genetic material

changes allele frequencies because it creates new alleles

the ultimate source of all genetic variation

caused by inaccurate DNA copying by cellular machinery and external agents altering DNA

Population Structure

person perspective- individuals in a population fall into genetically distinct groups

allele perspective- alleles are distributed across the population in some way other than expected due to change alone

Wright’s Fixation Indices

a system of three fixation indices, F, describes the genetic variation in a population as a reduction in heterozygosity relative to HWE

Fixation Index

the proportion of genetic variance attributed to the subpopulations relative to the total genetic variance

Wahlund’s Effect

reduction in heterozygosity in the meta-population due to population substructure

Migration

the movement of alleles among subpopulations

Island Model of Migration

focuses on one population and treats all other populations as one

One-Way Racism Model

offspring of mixed parentage are all members of one of the parental groups

Two-Way Racism Model

children of mixed parentage are distinct and form a new population of their own

Assortative Mating

choice of mate is dependent on a particular phenotype or genotype

Positive Assortative Mating/Homogamy

mating between people with like phenotypes/genotypes

Negative Assortative Mating

mating between people of unlike phenotypes/genotypes

Inbreeding

mating with a relative (individual)

mating between relatives occur more often than expected by chance (population)

affects all gene/loci across the genome

Inbreeding Coefficient

probability that both alleles (at a random locus) in an individual are identical by decent (autozygous)

Coefficient of Kinship

probability that two randomly chosen alleles in two different people are identical by descent or the average expected percentage identical by descent across the genome

measure of how closely related two people are

Anticipation

occurring earlier with each generation

Achromatopsia

colorblindness paired with extreme sensitivity to light and reduced visual acuity

caused by loss of function allele for CNGB3