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Branch
A line representing evolutionary relationships
Phylogeny
The evolutionary history of a species or group
Nodes
Points where branches split, representing common ancestors.
Tips
The endpoint of branches, representing living or extinct taxa
Internal Nodes
nodes within the tree, representing common ancestors of multiple taxa.
Clades
A group consisting of ancestor and all of its descendants.
Characters
observable traits used to infer phylogenetic relationships.
taxa
A group of organisms classified together
Synapomorphy
A shared derived character unique to a clade
monophyletic
a clade containing an ancestor and all of its descendants.
polyphyletic
a group containing species with different ancestors
outgroup
a taxon outside the group of interest used for comparison
ingroup
the group of taxa being studied
Homoplasy
A traits that arises independently in different lineages
Parsimony
the simplest explanation (fewest changes) is preferred
convergent evolution
Independent evolution of similar traits in different lineages
polytomy
A node with more than two branches, indicating uncertainty in relationships
evolutionary reversal
A return to an ancestral state
exaptation
A trait that evolved for one function but was co-opted for another.
genome
The complete set of genetic material in an organism
Pseudogenes
Non-functional gene copies
point mutations
A single nucleotide change
insertion
addition of DNA sequence
deletion
loss of DNA sequence
duplication
repetition of a DNA segment
Inversion
A segment is reversed within the chromosome
Chromosome fusion
Two chromosomes join into one
Aneuploidy
Abnormal number of chromosomes
Germ-line mutations
occur in reproductive cells; heritable
Somatic Mutations
occur in body cell; not heritable
genetic recombination
exchange of genetic material
independent assortment
random distribution of chromosomes during meiosis
genotype
Genetic makeup of an organism
Phenotype
observable traits of an organism
genetic polymorphism
the presence of multiple alleles in a population
quantitative traits
measurable characteristics that vary and influenced by genetics and environment
phenotypic plasticity
ability of an organism to change phenotype in response to the environment
polyphenism
distinct phenotypes produced by the same genotype under different conditions
Hardy-weinburg theorem
describing genetic equilibrium; important for understanding allele frequency changes.
Mechanisms of Allele frequency change
Mutation, genetic drift, gene flow, natural selection, and non-random mating
allele fixation
an allele reaches a frequency of 1.0 in a population; caused by selection or drift
genetic bottlenecks
population is established by a small number of individuals
genetic drift vs. natural selection
drift is strongest in small populations, selection is strongest with high fitness differences.
fitness
an organism’s reproductive success
relative fitness
fitness compared to other genotypes
inbreeding effects
increases homozygosity, exposing deleterious recessive alleles
experimental evolution
research using bacteria to study evolution over generations
mutations/selection balance
explains persistence of rare deleterious alleles
genetic variation maintenance
mutation, gene flow, balancing selection
Balancing selection
negative frequency-dependent selection and heterozygote advantage
variation
differences in traits among individuals
heritability
the proportion of trait variation due to genetics
selection types
directional, stabilizing, and disruptive selection
selection strength
weak selection: slow evolutionary change. Strong selection: rapid evolutionary change.
darwin’s finches
example of natural selection. finches evolved different beak shapes and sizes depending on their food sources.
pocket mouse example
natural selection and adaptation to environment
fitness landscape (scarlet king snake)
fitness varies with geography; gene flow spreads alleles
dual selection pressures on plants
birds and wasps exert opposing selection forces.
Human driven selection
artificial selection, extended phenotype, and chemical warfare
