BILD 003 midterm vocab

Lineage

A series of ancestors and descendants connected through evolutionary history.

Trait (character)

A feature or characteristic of an organism that can be studied and compared.

Homology

A similarity between organisms caused by inheritance from a common ancestor.

Convergent evolution

The independent evolution of similar traits in different evolutionary lineages.

Descent with modification

The idea that species descend from ancestors but accumulate changes over generations.

Divergence

The process in which related populations or lineages become increasingly different.

Evolution

A change in allele frequencies in a population across generations.

Natural selection

An evolutionary process in which individuals with certain heritable traits have greater reproductive success.

Mutation

A change in DNA that can create a new allele and introduce genetic variation.

Genetic drift

Random changes in allele frequencies caused by chance sampling in a population.

Gene flow

The movement of alleles between populations through migration and reproduction.

Artificial selection

Human-directed breeding in which organisms with desired traits are chosen to reproduce.

Dispersal

The movement of organisms into a new geographic area where they may establish a population.

Biogeography

The study of the geographic distribution of organisms across Earth.

Gradual geological change

The idea that Earth's geological features are shaped by slow processes over long periods.

Principle of succession

The pattern in which fossil organisms in a region resemble living organisms from that same region.

Adaptive radiation

The diversification of one ancestral lineage into multiple species adapted to different ecological niches.

Local adaptation

The evolution of traits that improve fitness in a particular local environment.

Population

A group of individuals of the same species living in an area and potentially interbreeding.

Gene pool

The complete collection of alleles present in a population.

Allele

A version of a gene.

Allele frequency

The proportion of all copies of a gene in a population that are a particular allele.

Genotype

The combination of alleles an individual has for a particular gene.

Genotype frequency

The proportion of individuals in a population that have a particular genotype.

Genotype count

The number of individuals in a population with a particular genotype.

Homozygous

Having two identical alleles for a particular gene, such as AA or aa.

Heterozygous

Having two different alleles for a particular gene, such as Aa.

Dominant allele

An allele whose effect is expressed in a heterozygote under complete dominance.

Recessive allele

An allele whose effect is masked in a heterozygote under complete dominance.

Hardy-Weinberg Equilibrium (HWE)

A model describing genotype frequencies in a population when specified evolutionary conditions are met.

p

The frequency of one allele in a two-allele system.

q

The frequency of the other allele in a two-allele system.

Allele frequency equation

The equation p + q = 1, representing the total frequency of two alleles.

Hardy-Weinberg equation

The equation p² + 2pq + q² = 1, predicting genotype frequencies under HWE.

p²

The expected frequency of the homozygous genotype AA under HWE.

2pq

The expected frequency of the heterozygous genotype Aa under HWE.

q²

The expected frequency of the homozygous genotype aa under HWE.

Expected genotype count

The expected genotype frequency multiplied by the total number of individuals.

Observed genotype count

The actual number of individuals found with each genotype in a population sample.

Chi-squared goodness-of-fit test

A statistical test comparing observed counts with expected counts.

Evolutionary processes

Processes that can change allele frequencies, including mutation, gene flow, genetic drift, and natural selection.

Nonrandom mating

A mating pattern in which individuals do not pair by chance with respect to particular traits or genotypes.

Assortative mating

Nonrandom mating in which individuals with similar traits are more likely to mate.

Disassortative mating

Nonrandom mating in which individuals with different traits are more likely to mate.

Bottleneck effect

A type of genetic drift caused by a sharp reduction in population size.

Founder effect

A type of genetic drift that occurs when a small group establishes a new population.

Genetic diversity

The variety of alleles or genetic differences present in a population.

Fixation

The condition in which an allele reaches a frequency of 1, meaning it is the only allele at that gene in the population.

Loss of an allele

When an allele reaches a frequency of 0 and is no longer present in a population.

Fitness

An organism's relative contribution of viable offspring to future generations.

Heritability

The extent to which differences in a trait are passed from parents to offspring through genetic inheritance.

Phenotype

An organism's observable characteristics, influenced by its genes and environment.

Phenotypic variation

Differences in observable traits among individuals in a population.

Histogram

A graph showing the frequency or distribution of values for a trait.

Directional selection

Natural selection that favors one extreme phenotype and shifts the population mean toward that extreme.

Stabilizing selection

Natural selection that favors intermediate phenotypes and selects against both extremes.

Disruptive selection

Natural selection that favors both extreme phenotypes over intermediate phenotypes.

Population mean

The average value of a particular trait in a population.

Balancing selection

Natural selection that maintains multiple alleles or phenotypes in a population.

Heterozygote advantage

A form of balancing selection in which heterozygotes have higher fitness than either homozygote.

Negative frequency-dependent selection

A form of selection in which a phenotype has higher fitness when it is less common.

Phylogenetics

The study of evolutionary relationships among organisms.

Phylogenetic tree

A branching diagram representing a hypothesis about evolutionary relationships.

Taxon

A named group of organisms; the plural is taxa.

Branch

A line on a phylogenetic tree representing an evolutionary lineage.

Branchpoint (node)

A point on a phylogenetic tree where one lineage splits into two or more lineages.

Root

The base of a phylogenetic tree representing the common ancestor of the groups shown.

Most recent common ancestor

The closest shared ancestor of two or more taxa on a phylogenetic tree.

Sister taxa

Two taxa that share an immediate common ancestor with each other.

Topology

The branching pattern of a phylogenetic tree, showing relationships among taxa.

Branch length

The length of a branch, which may represent time or evolutionary change depending on the tree.

Parenthetical notation

A system using nested parentheses to represent the branching relationships in a phylogenetic tree.

Monophyletic group

A group containing a common ancestor and all of its descendants.

Non-monophyletic group

A grouping that does not include all descendants of its common ancestor or combines taxa without including their proper shared ancestry.

Character transition

An evolutionary change in a trait along a lineage.

Parsimony

The principle of preferring the phylogenetic tree that requires the fewest evolutionary changes.

Nested hierarchical classification

An organizational system that places smaller groups within larger groups based on shared characteristics.

Species

A group or lineage of organisms classified as distinct from other such groups.

Biological Species Concept

The definition of a species as populations that can interbreed and produce viable, fertile offspring.

Morphological Species Concept

A species concept that identifies species using physical form and structural characteristics.

Ecological Species Concept

A species concept that identifies species based on their ecological niche.

Gene flow within a species

The exchange of alleles among interbreeding populations that helps genetically connect them.

Reproductive isolation

The prevention of successful gene exchange between populations through reproduction.

Prezygotic barrier

A reproductive barrier that prevents mating or fertilization before a zygote forms.

Postzygotic barrier

A reproductive barrier that acts after fertilization and reduces hybrid survival or reproduction.

Habitat isolation

A prezygotic barrier in which populations live in different habitats and rarely encounter each other to mate.

Temporal isolation

A prezygotic barrier in which populations reproduce at different times.

Behavioral isolation

A prezygotic barrier in which differences in courtship or mating behavior prevent reproduction.

Mechanical isolation

A prezygotic barrier in which reproductive structures are incompatible.

Gametic isolation

A prezygotic barrier in which sperm and egg cannot successfully fuse.

Hybrid

An offspring produced by individuals from different species or genetically distinct populations.

Hybrid sterility

A postzygotic barrier in which hybrid offspring survive but cannot reproduce successfully.

Speciation

The evolutionary process through which new species form.

Allopatric speciation

Speciation that occurs when populations become geographically separated and gene flow is reduced or stopped.

Sympatric speciation

Speciation that occurs without geographic separation between populations.

Geographic isolation

The physical separation of populations by a geographic barrier or distance.

Essentialism

The idea that species have fixed, unchanging defining characteristics.

Polyploidy

The condition of having more than two complete sets of chromosomes; it can contribute to speciation, especially in plants.

Reproductive isolation evolution

The gradual accumulation of differences that eventually prevents populations from successfully exchanging genes.