Evolutionary Biology Unit 2

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