Evolution Terms

Biogeography

The geographic distribution of living organisms

Common Ancestry

The concept that if you trace back the lineages of living species far enough in time, those species will converge to a shared ancestor

Evolution

The change in frequency of genetic variants in a population

Homology

Traits whose similarities are explained by common ancestry

Natural Selection

The tendency for genetic variants that enhance fitness to go to fixation and variants that reduce fitness to be lost from populations (survival of the fittest)

Nested Hierarchy

A pattern of groups nested within groups (without overlaps) as seen in taxonomies and classification systems

Taxonomies

Systems for classifying organisms based on shared characteristics and evolutionary relationships.

Polymorphism

The existence of multiple variants within a population

Transitional Fossil

Fossil taxa that have some, but not all, of the derived traits of a living group

Allele Frequency

The proportion of all alleles at a locus that are of a particular type

Allele

A variant of a gene

Diploid

Having two sets of chromosomes

Evolution

Change in the genetic composition of a population over time (change in allele frequencies)

Fixed

An allele that has a frequency of 1.0 in a population

Genotype

Genetic makeup of an organism

Haploid

The trait of having one set of chromosomes in an organism

Hardy Weinberg Law

The law used to predict the genotype frequencies in a population for the next generation, based on the allele frequencies in the current generation

Locus

A place in the genome where alleles reside; in diploids, each individual has two alleles per locus

Phenotype

The physical and behavioral characteristics of an organism that result from the interaction of the organism’s genotype and its environment

Polymorphic

When more than one allele is found at a given locus in a population

Populations

A group of inbreeding organisms

Selfing

When an organism reproduces with itself, providing both the egg and sperm components

Beneficial mutation

A new allele that ENHANCES the fitness of an organism

Deleterious mutation

A new allele that DECREASES the fitness of an organism

Directional selection

Selection that arises when one allele consistently raises fitness, eventually leading to fixation of that beneficial allele

Mutation

A change in a gene sequence

Neutral mutation

A new allele with neither a beneficial nor a deleterious effect

Relative fitness

The fitness of a given genotype divided by the fitness of a reference genotype that is assigned to be 1.0

Genetic bottleneck

The phenomenon in which a population lineage shrinks to a small size for a period of time, causing that population to lose genetic variation

Genetic drift

RANDOM changes in allele frequencies in a population over time

Genetic load

The frequency of deleterious alleles that have accumulated in a population

Fitness

The expected reproductive output of a genotype

Genetic Disorders

Diseases caused by changes at a single genetic locus that reduce fitness

Branch

The lines that make up a tree diagram that represent population lineages

Clade

All the descendants of a single ancestral lineage

Lineage splitting

A splitting of a population into genetically separate populations that no longer have gene flow

Node

Branching points of tree diagrams that represent lineage splitting

Phylogenic tree

A branching diagram used to represent evolutionary relationships and relatedness between different organisms based on their common ancestry

Pruning

Removing tips/taxa or clades from a tree without changing the topology

Root

The base of the tree that represents the common ancestral lineage of all taxa in the tree

Speciation

Lineage splitting that leads to taxa being classified as separate species

Taxon (plural = taxa)

A named group of biological organisms at the tips of a tree

Tree thinking

The ability to use the metaphor of a phylogenetic tree to convey accurate evolutionary information

Tree topology

A list of all the clades that a tree contains