Bio 104 1-3

Evolution

Change in inherited traits (allele frequencies) of a population over generations.

Microevolution

Evolution within a population or species (small-scale).

Macroevolution

Large-scale evolution above the species level; origin of new species and clades.

Population

Group of interbreeding individuals of one species living in a given area.

Gene Pool

Total collection of alleles in a population.

Allele Frequency

Proportion of one allele among all alleles for a gene.

Genotype

Genetic makeup (e.g., AA, Aa, aa).

Phenotype

Physical expression of genotype.

Locus

Location of a gene on a chromosome.

Allele

Variant of a gene.

Homozygous / Heterozygous

Two same alleles / two different alleles.

Hardy–Weinberg Equilibrium (HWE)

Null model showing when evolution does not occur.

Null Model

Baseline expectation used to detect evolution.

Mutation

Random change in DNA → new alleles.

Migration (Gene Flow)

Movement of individuals or alleles between populations.

Genetic Drift

Random change in allele frequencies (strongest in small populations).

Founder Effect

Small group establishes new population → low genetic diversity.

Bottleneck Effect

Population drastically reduced → loss of genetic variation.

Natural Selection

Nonrandom process favoring traits that increase survival/fecundity.

Adaptation

Trait that improves survival or reproduction.

Fecundity

Ability to produce offspring.

Fitness (Darwinian)

Survival + fecundity.

Speciation

Process by which one species splits into two or more distinct species.

Species

Group of organisms capable of interbreeding and producing fertile offspring.

Anagenesis

Evolutionary change within a single lineage (no split).

Cladogenesis

Splitting of one lineage into two (new species).

Biological Species Concept (BSC)

Species = populations that can interbreed and are reproductively isolated.

Evolutionary Species Concept

Lineage evolving separately with its own historical fate.

General Lineage Concept

Species = separately evolving lineages.

Cryptic Species

Morphologically identical but genetically distinct.

Polymorphism

Multiple distinct forms within one species.

Sexual Dimorphism

Male and female forms differ.

Prezygotic Isolation

Barriers preventing fertilization before it occurs.

Postzygotic Isolation

Barriers preventing hybrid viability or fertility after fertilization.

Allopatric Speciation

Populations separated by a physical barrier → divergence.

Vicariance

Barrier forms and splits an existing population.

Dispersal

Individuals cross a barrier and start a new population.

Parapatric Speciation

Adjacent populations diverge along environmental gradient.

Sympatric Speciation

Divergence within same area due to disruptive selection.

Polyploidy

Doubling of chromosome sets → instant reproductive isolation.

Autopolyploidy

Within one species (chromosomes fail to separate).

Allopolyploidy

Between two species (hybridization + doubling).

Nondisjunction

Error in meiosis creating gametes with extra chromosomes.

Dobzhansky–Muller Model

Genetic incompatibility evolves between isolated populations.

Reinforcement

Selection strengthens prezygotic barriers when hybrids are less fit.

Phylogeny

Evolutionary history of a group or lineage.

Phylogenetic Tree

Visual representation of evolutionary relationships.

Root

Common ancestor of all taxa on the tree.

Node

Branching point = speciation event.

Branch

Lineage evolving through time.

Tip

Existing species.

MRCA (Most Recent Common Ancestor)

Most recent ancestor shared by two or more lineages.

Clade (Monophyletic Group)

Ancestor + all descendants.

Paraphyletic Group

Ancestor but not all descendants.

Polyphyletic Group

Group without common ancestor (assembled by similarity).

Character

Heritable feature used to infer relationships.

Character State

Variation of a character.

Synapomorphy

Shared derived trait that defines a clade.

Homology

Similarity due to shared ancestry.

Homoplasy

Similarity due to convergence, not ancestry.

Outgroup

Closely related taxon used to determine ancestral vs. derived traits.

Character Polarity

Direction of evolution (ancestral → derived).

Parsimony

Simplest tree (fewest changes) preferred.

Homoplasy Conflict

Trait evolves twice or is lost twice.

Heuristic Search

Algorithm that finds best tree when too many possible trees exist.

Jukes–Cantor (JC)

All nucleotide substitutions equally probable.

Kimura Two-Parameter (K2P)

Transitions and transversions occur at different rates.

Orthologs

Homologous genes diverged by speciation.

Paralogs

Homologous genes diverged by duplication.

Incomplete Lineage Sorting (ILS)

Gene trees differ from species trees due to ancestral polymorphism.

Deep Coalescence

Same as ILS—ancestral variation persists through speciation.