Unit 7 Natural Selection

Evolution

change in the genetic makeup of a population over time; descent with modification

Descent with modification

heritable traits change from generation to generation

Natural selection

a process in which individuals that have certain traits tend to survive and reproduce at higher rates than other individuals because of those traits

Adaptations

inherited characteristics of organisms that enhance their survival and reproduction

Differential survival

the traits that lead to survival (“favorable” traits) will accumulate in the population

Artificial selection

the selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

Population

a group of individuals of the same species that live in the same area and interbreed to produce fertile offspring

Gene pool

a population’s genetic makeup

Microevolution

small scale genetic changes in a population (driven by mutations, genetic drift, migration/gene flow, natural selection)

Genetic drift

chance events that cause a change in allele frequency from one generation to the next

Mutations

changes in the DNA sequence that can lead to new traits and variations in a population

Bottleneck effect

when a large population is drastically reduced by a non-selective disaster (flood, fire, etc)

Founder effect

when a few individuals become isolated from a large population and establish a new small population with a gene pool that differs from the large population

Gene flow

the transfer of alleles into or out of a population due to fertile individuals or gametes

Relative fitness

the number of surviving offspring that an individual produces compared to the number left by others in the population

Directional selection

when a single phenotypic trait is favored, causing it to shift in one direction over time, often in response to environmental changes

Stabilizing selection

a form of natural selection that favors intermediate variants by acting against extreme phenotypes

Disruptive selection

a form of natural selection that favors extreme phenotypes at both ends of the spectrum, leading to increased diversity within a population

Sexual selection

a type of natural selection that explains why many species have unique/showy traits

Hardy Weinberg Equilibrium

a model used to assess whether natural selection or other factors are causing evolution at a particular locus: frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

p + q = 1

represents the relationship between allele frequencies in a population, where p is the frequency of the dominant allele and q is the frequency of the recessive allele

p² + 2pq + q² = 1

describes the expected frequencies of genotypes in a population, where p² is the percentage of homozygous dominant, 2pq is the percentage of heterozygous, and q² is the percentage of homozygous recessive individuals

Fossils

remains or traces of past organisms

Fossil record

gives a visual of evolutionary change over time

Comparative morphology

analysis of the structures of living and extinct organisms

Homology

characteristics in related species that have similarities even if the functions differ

Embryonic homology

many species have similar embryonic development

Vestigial structures

structures that are conserved even though they no longer have a use (tailbone and appendix in humans)

Molecular homology

many species share similar DNA and amino acid sequences

Homologous structures

characteristics that are similar in two species because they share a common ancestor (arm bones of many species)

Convergent evolution

similar adaptations that have evolved in distantly related organisms due to similar environments

Analogous structures

structures that are similar but have separate evolutionary origins (wings in birds vs bats vs bees)

Biogeography

the distribution of animals and plants geographically

Systematics

classification of organisms and determining their evolutionary relationships

Taxonomy

naming and classifying species

Phylogenetics

hypothesis of evolutionary history

Phylogenetic trees

diagrams that represent the evolutionary history of a group of organisms

Nodes

represent common ancestors

Root

the common ancestor of all the species

Sister taxa

two clades that emerge from the same node

Basal taxon

a lineage that evolved from the root and remains unbranched

Synapomorphy

a derived character shared by clade members

Derived characteristic

similarity inherited from the most recent common ancestor of an entire group

Ancestral characteristic

similarity that arose prior to the common ancestor

Outgroup

a lineage that is the least closely related to the rest of the organisms

Monophyletic group

includes the most recent common ancestor of the group and all of its descendants (clade)

Paraphyletic group

includes the most recent common ancestor of the group, but not all its descendants

Polyphyletic group

does not include the most recent common ancestor of all members of the group

Principle of parsimony

use the hypothesis that requires the fewest assumptions (DNA changes)

Species

a group able to interbreed and produce viable, fertile offspring

Speciation

formation of new species

Allopatric speciation

physical barrier divides population or a small population is separated from main population

Sympatric speciation

a new species evolves while still inhabiting the same geographic region as the ancestral species

Prezygotic barriers

prevent mating or hinder fertilization

Habitat isolation

species live in different areas or they occupy different habitats within the same area

Temporal isolation

species breed at different times of the day, year, or season

Behavioral isolation

unique behavioral patterns and rituals separate species

Mechanical isolation

the reproductive anatomy of one species does not fit with the anatomy of another species

Gametic isolation

proteins on the surface of gametes do not allow for the egg and sperm to fuse

Postzygotic barriers

prevent a hybrid zygote from developing into a viable, fertile adult

Reduced hybrid viability

the genes of different parent species may interact in ways that impair the hybrid’s development or survival

Reduced hybrid fertility

a hybrid can develop into a healthy adult, but it is sterile, usually results due to differences in number of chromosomes between parents

Hybrid breakdown

the hybrid of the first generation may be fertile, but when they mate with a parent species or one another, their offspring will be sterile

Microevolution

change in allele frequencies within a single species or population (natural and sexual selection, genetic drift, gene flow)

Macroevolution

large evolutionary patterns (adaptive radiation, mass extinction)

Punctuated equilibrium

when evolution occurs rapidly after a long period of stasis

Gradualism

when evolution occurs slowly over hundreds, thousands, or millions of years

Divergent evolution

groups with the same common ancestor evolve and accumulate differences resulting in the formation of a new species

Adaptive radiation

if a new habitat or niche becomes available, species can diversify rapidly

Convergent evolution

two different species develop similar traits despite having different ancestors

Extinction

the termination of a species

RNA World Hypothesis

proposes that RNA could have been the earliest genetic material