Term Test 2 Flashcards
Evolution by selection
-Changes in allele frequency
-Natural selection typically takes many generations to have a substantial impact.
-Rate of change is a function of selection intensity
patterns of selection
- recessive vs dominant alleles
- heterozygous favoured
- homozygous favoured
- frequency dependent selection
evolution by mutation
-Mutation is the source of all new alleles and genes and provides the raw material for evolution
-Mutation can cause substantial changes in allele frequencies, but only over really long periods of time
-Mutation-selection balance
-Many mutations are deleterious
- Selection may remove deleterious alleles but mutation may re-introduce them, hence they persist.
- When the rate at which new copies of a deleterious
allele are produced by mutation equals the rate at
which selection removes them, there is a mutation-
selection balance
gene flow
May be caused by:
-Dispersal- one-way movement of a juvenile individual away from the place of their birth.
-Transport of pollen, seeds, spores by any means (e.g., wind, animals, water, etc.)
-Tends to homogenize allele frequencies among populations.
-Therefore, tends to prevent evolutionary divergence of populations.
-May function to decrease the population level impact of natural selection and/or other mechanisms of evolution
-FST (the fixation index) is a measure of variation among populations in allele frequencies at a locus
-Gene flow reduces Fst among populations
genetic drift
-Random, unpredictable changes in allele frequencies from one generation to the next.
-“blind luck”
-Mechanism of evolution resulting from random sampling of gametes from one generation to the next
-Genetic drift is sampling error across generations
-From Hardy-Weinberg perspective, it results from a violation of the assumption of infinite population size.
-Incidence and rate of genetic drift increases as population size decreases
-Does not lead to adaptation (as does natural selection).
-Natural selection happens for a reason: i.e., alleles that produce certain phenotypes are more successful (i.e., fit) in particular environments, and therefore increase in frequency
-For genetic drift allele frequency changes happen by ‘chance’
-typically leads to fixation (loss of alleles) and a decline in heterozygosity
-Demographic events that can cause genetic drift:
1. Founder events – may be considered a form of genetic drift.
-Occur when a new population is founded by a small group of individuals
2. Bottleneck– a sharp decline in population size followed by population recovery
non-random mating
- inbreeding
-mating among closely-related individuals.
-Results in increase in the frequency of homozygotes in a population, relative to what is expected based upon H-W assumptions
-Inbreeding alters genotype frequencies.
-But it does not alter allele frequencies.
-Therefore, on its own non-random mating is NOT a mechanism of evolution - outbreeding
-mating among highly unrelated individuals - positive assortative mating
-between individuals with similar phenotypes (large individuals mate with large individuals) - negative assortative mating
-between individuals with dissimilar phenotypes (large individuals mate with small individuals)
-does not, on its own, change allele frequencies.
-It does impact genotype frequencies, so in concert with natural selection, it can have important evolutionary consequences
agents of evolution
- Selection- can change allele and genotype frequencies
- Mutation- weak evolutionary force but provides the raw variation for evolution
- Gene flow (i.e., ”migration”)-when source and recipient populations differ in allele frequencies,
migration can cause recipient population to evolve
-Tends to homogenize allele frequencies among
populations - Genetic drift-random shift in allele and genotype frequencies
- Non-random mating- does not change allele frequencies, but does change genotype frequencies.
- Can effect evolution in concert with natural selection.
what is phylogenetics
the study of ancestor descendent relationships. The objective of phylogeneticists is to construct phylogenies
what is phylogeny
A hypothesis of ancestor descendent relationships
what is a phylogenetic tree
a graphical summary of a phylogeny
-Also called an evolutionary tree
what is plesiomorphy
refers to the ancestral character state
what is apomorphy
character state different than the ancestral state, or DERIVED STATE
what is a synapomorphy
a derived character state (apomorphy) that is SHARED by two or more taxa due to inheritance from a common ancestor: these character states are phylogenetically informative using the parsimony or cladistic criterion
what is autapomorphy
a uniquely derived character state
what is homoplasy
Homoplasy describes similarity of character state state due to independent evolution
