BIO 152 - Evolution

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

Fixation

the loss of all variants except one from 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

Nested hierarchy

a pattern of groups nested within groups (without overlap) as seen in taxonomies

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

Branch

the lines that make up a tree diagram, which represent population lineages

Clade

all the descendants of an ancestral lineage

Lineage splitting

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

often due to geographic isolation or a rare event of dispersal

Node

branching points of tree diagrams, which represent lineage splitting

Phylogenetic Tree

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

Pruning

removing tips or clades from a tree without changing the topology

Root

the base of a tree, representing the common ancestral lineage of all taxa in the tree

Speciation

lineage splitting that ultimately leads to taxa that are classified as separate species

Taxon

a named group of biological organisms, often shown 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

Convergent evolution

the phenomenon observed in phylogenetic trees where the same trait evolves separately in more than one lineage; although they appear similar, these traits are not homologous

Homologous

a descriptor of a character shared in separate species that was inherited from the common ancestor of those species

Principle of parsimony

the idea that given multiple alternative hypotheses, the most likely hypothesis is the one that makes the fewest assumptions; in relation to phylogenies, parsimony favors the scenario that invokes the minimum number of evolutionary changes (character loss/gain)

Reversal

the phenomenon in which an ancestral trait was lost and then re-evolved along a lineage

Separate ancestry

the alternative hypothesis to common ancestry, which propose that each living taxon has an independent origin

Allele frequency

in a population, the proportion of all alleles at a locus that are of a particular type

Allele

a particular variant of a gene

Diploid

the trait of having two sets of chromosomes, as in humans

Evolution

change in the genetic composition of a population over time

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 that, when a few key assumptions hold, makes it possible 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 the environment

Polymorphic

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

Populations

a group of interbreeding 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 organisms

Deleterious mutation

a new allele that decreases organismal fitness

Directional selection

selection that arises when one allele consistently raises fitness; eventually the beneficial allele is expected to become fixed in the population

Mutation

a change in a gene sequence; arises independent of the needs of the organism

Natural selection

the process of allele frequency change due to fitness variation among genotypes at that locus

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, which relative fitness is assigned to be 1.0

Genetic bottleneck

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

Genetic drift

random change in allele frequencies in a population over time

Genetic load

the frequency of deleterious alleles that have accumulated in a population

Carrier

An individual who is heterozygous for a disease

Overdominant selection

Selection in which heterozygote genotypes have the highest fitness

Trans-specific polymorphisms

A set of alleles that are shared between closely related species; they arose before speciation and were maintained as polymorphisms

Underdominant selection

Selection in which heterozygote genotypes have the lowest fitness

Continuous trait

a trait that is characterized by values on a continuous scale, rather than being controlled by a single locus

Disruptive selection

selection that favors trait values at both extremes of the trait value distribution

Heritability (h²)

the fraction of the variation in a population that can be explained by genetics

Response to selection (r)

the amount the mean trait value in a population changes after one generation

Stabilizing selection

selection that disfavors extreme trait values and favors trait values towards the center of the trait distribution

Standard deviation

Square root of the variance

Variance

a measure of the spread of the distribution of a trait values in a population (technically, the sum of the squared deviations from the mean value)_

Altruistic behavior

actions (or tendencies to act) that result in the organism exhibiting the behavior lowering its own fitness while increasing the fitness of other organisms within its population

Exaggerated secondary sexual characteristics

dramatic traits in an organism that lower the organism’s viability but evolve because they are favored by sexual selection

Exaptation

the phenomenon in which a trait that evolved for one function is currently used for a different function

Polygamy

the phenomenon in which one male can mate with many females

Runaway sexual selection

the phenomenon in which secondary sexual characteristics become exaggerated due to feedback between male traits and female preferences (or, more rarely, female traits and male preferences).

Allopatric speciation

speciation driven by geographic isolation

Assortative mating

the phenomenon in which individual organisms tend to mate with other organisms with trait values like theirs

Biological Species Concept

the view that species are defined by the ability of their members to reproduce with one another and to be unable to reproduce with the members of other speices

Clinal variation

gradual changes in traits as a function of geographical separation

Discrete variation

genetic variation among geographically separated populations, where each population contains genetically similar individuals

Extrinsic reproductive isolation

the phenomenon in which two organisms are no longer able to reproduce due to geographic separation

Intrinsic reproductive isolation

the phenomenon in which two organisms are no longer able to reproduce, even when they are allowed to encounter one another

Phylogenetic species concept

the view that species are clades (monophyletic groups), like other in the taxonomic hierarchy (genera, subspecies, etc.), that biologists have chosen to assign to the species rank for practical reasons

Speciation

the splitting of ancestral species into descendant species

Sympatric speciation

speciation without geographic separation, driven by assortative mating within a population

Anoxygenic photosynthesis

the reduction of carbon dioxide to organic molecules using light energy in which something other than water is the electron donor and oxygen gas is not released

Autogenous hypothesis for eukaryotes

the theory that mitochondria and nucleus both evolved within the same eukaryotic lineages

Cyanobacteria

a clade of bacteria characterized by its ability to perform oxygenic photosynthesis

Endosymbiosis

the phenomenon in which a prokaryotic cell comes to live and divide within a host cell

Endosymbiotic hypothesis for eukaryotes

the theory that mitochondria are derived from endosymbiotic bacteria taken up by the host cell whose genome is found in the eukaryotic nucleus

Eukaryotic cells

a category of cells characterized by an outer membrane and many internal membrane-boudn compartments including the mitochondria and nucleus

Inside-out model

a theory for development of eukaryotic internal compartments that suggests that the outer plasma membrane of a prokaryotic ancestor was pushed outward and ultimately fused to create the cytoplasm and plasma membrane of eukaryotes

Last Universal Common Ancestor (LUCA)

the most recent ancestor of all known life

Organelle

memrane-bound compartment of a eukaryotic cell

Outside-in model

a theory for development of eukaryotes that starts with the production of vesicles within the cytoplasms by internalization

Oxygenic photosynthesis

the reduction of carbon dioxide to organic molecules using light energy in which water is the electron donor and oxygen gas is released

Prokaryotic cells

a category of cells characterized by an outer membrane containing no internal membrane structures

Admixture

the mating of two individuals from genetically distinct groups

Arboreal

the mating of two individuals from genetically distinct groups

Diurnal

the characteristic of being active during the day

Historical contingency

a randoms eries of events with unintended consequences

Introgression

the transfer of genetic information between species