Unit 7: Natural Selection

• Evolution: a change in the genetic composition (allele frequencies) of a population over time
• Theory: A hypothesis that has been tested and supported with a significant amount of data
• raw material of evolution: genetic variation
• origin of genetic variation: genetic mutation
• genetic variation: Differences among individuals in the composition of their genes or other DNA segments
• Adaptation: A trait that helps an organism survive and reproduce
• Population: A group of individuals of a single species that live in a particular geographic area at the same time
• Alleles: Different forms of a gene (eg. B, b)
• gene pool: sum of all copies of all alleles at all loci in a population (all the B and b)
• allele frequency: proportion of each allele in the gene pool (eg. 80/100=0.80)
• genotype frequency: proportion of each genotype among individuals in the population
• artificial selection: Selection by humans for breeding of useful traits from the natural variation among different organisms
• natural selection: A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
• Factors that drive natural selection: 1.) more individuals are born that survive and reproduce 2.) offspring resemble their parents but aren't identical 3.) differences among individuals that affect their chance of survival and reproduction
• fossil record: Chronological collection of life's remains in sedimentary rock layers
• convergent evolution: different species evolve similarly in the same type of environment (eg. sharks & dolphins have similar traits, but evolved independently)
• analogous structures: Body parts that share a common function, but not structure/origin (eg. insect wings and bird wings)
• vestigial organs/structures: organ that serves no or a changed function in organism, organ so reduced in size, it does not serve an important function; may be homologous to structures in other organisms

  ex; human appendix
• genetic drift: random change in allele frequencies from one generation to the next usually cause by random events (such as the effect of small populations)
• population bottleneck: Genetic drift where an environmental event results in survival of only a few individuals (which can have an effect on allele frequencies in the population and can result in a loss of genetic variation)
• founder effect: Genetic drift that changes allele frequencies when a few individuals colonize a new area
• nonrandom mating: Mating among individuals on the basis of their phenotypic similarities or differences, rather than mating on a random basis (aka its basically inbreeding)
• 5 causes of genetic change: 1.) mutation 2.) gene flow 3.) nonrandom mating 4.) genetic drift 5.) selection
• gene flow

  movement of alleles between populations (eg. migration)
• Hardy-Weinberg equilibrium: a model in which allele frequencies do not change across generations and genotype frequencies can be predicted from allele frequencies
• 5 Hardy-Weinberg conditions:

  1. Mating is random

  2. population size in infinite (no genetic drift)

  3. no gene flow

  4. no mutations

  5. No selection of genotypes
• stabilizing selection: Selection that favors average individuals (eg. bird eggs, human birth weight)
• directional selection: Selection that favors individuals that vary in one direction from the mean (eg. dark coloration, early blooming plants)
• disruptive selection: Selection that favors individuals that vary in both directions from the mean (eg. middle individual has poor camouflage)
• molecular clock: Model that uses DNA comparisons to estimate the length of time that two species have been evolving independently
• Phylogeny: The evolutionary history of a species or group of related species
• Phylogenetic tree: Diagrammatic reconstructuon of evolutionary history
• Node :When a single lineage divides into 2
• The timing of splitting events are shown by what on a phylogenic tree? Position of nodes on the time axis
• Taxon: any group of species that we designate with a name
• Sister clades: two clades that are each other's closest relatives
• Ancestral trait: characteristic that existed in an ancestor
• derived trait: newly evolved features that do not appear in the fossils of common ancestors
• Homologous features are: -shared by two or more species

  -inherited from a common ancestor
• Outgroup: Species or group known to be closely related to, but phylogenetically outside of, the group of interest