Unit 1- Evolution

evolution

change in genetic composition of a population from generation to generation

darwin’s observations

• populations have varying traits

• traits are heritable

• not all offspring survive into adulthood due to limited resources

darwin’s conclusion

individuals with traits advantageous in survival and reproduction are able to have more offspring, leading to the accumulation of advantageous traits in future generations

adaptation

inherited characteristic that enhances survival/reproduction in specific environments

coevolution

reciprocal evolution between interacting species

macroevolution

big evolutionary changes over long periods of time; above species

microevolution

small evolutionary changes over short period of time; within species

Homologous structures

structures in different species that are similar due to common ancestry

Vestigial structures

homologous structures that are present in an organism but are no longer used

Convergent evolution

organisms independently adapt to similar environments in a similar way

Analogous structures

structures in different species that are similar due to adaptation to similar environments

types of homology

anatomical, developmental, molecular

Comparative embryology

anatomical homologies not visible in adult organisms

Molecular homology

similarities in DNA sequences or amino acid sequences due to common ancestry

Evidence for evolution

homology, fossil record, biogeography, observation

Fossil record

provides evidence of extinction of species, the origin of new groups, and changes within groups over time

geological timescale

radioactive decay, relative layer, chemical dating

Biogeography

related species are usually found near each other

artificial selection

humans breed for specific traits

Direct observation

observable, measurable changes over short periods of time

chi square analysis

how well does data fit experimental expectations?

X² < CV

• observed vs expected values are NOT statistically significantly different

• accept the null hypothesis

X² < CV

• observed vs expected values ARE statistically significantly different

• reject the null hypothesis

Relative fitness

contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

Directional selection

conditions favor individuals exhibiting one extreme of the trait

stabilizing selection

favors intermediate phenotype and extremes selected against

disruptive selection

conditions favor both extremes of the phenotype, intermediate selected against

sexual selection

one sex chooses favorable traits in the other

sexual dimorphism

difference in size/appearance between sexes

taxonomy

domain, kingdoms, phylum, class, order, family, genus, species

biological species concept

a group of individuals capable of interbreeding and producing viable, fertile offspring

issues with biological species concept

fossils, hybrids, asexual reproduction, molecular differences

speciation

formation of distinct species

gradualism

evolution proceeds by accumulation of gradual changes; constant rate

punctuated equilibrium

periods of rapid speciation and periods of no change; variable rate

allopatric speciation

a population is divided by a geographic barrier

sympatric speciation

one species becomes 2+ while living in the same geographic region

adaptive radiation

many new species diversity rapidly from a common ancestor, often when changes lead to new niches

pre-zygotic isolation

temporal, behavioral, habitat, mechanical, gametic

habitat (ecological) isolation

inhabit different niches in same region

temporal isolation

mate during different seasons or time of day

behavioral isolation

unique behaviors identify and attract same species

mechanical isolation

parts don’t fit

gametic isolation

egg and sperm do not fuse into zygote

post-zygotic isolation

reduced viability, reduced fertility, hybrid breakdown

reduced hybrid variability

hybrids fail to develop or are frail

reduced hybrid fertility

hybrids cannot reproduce/are sterile

hybrid breakdown

1st gen viable, but not future gens

clade

group of all organisms descended from a common ancestor

outgroup

organism not in the group whose evolutionary relationships are being investigated; furthest related and first to branch off

Cladograms

organisms grouped by traits (DNA) shared by their common ancestors

species

can interbreed in nature and produce fertile, viable offspring

population

group of individuals in the same species living in the same area

gene flow

individuals emigrating from one population and immigrating to another populations

genetic drift

chance events that cause allele frequencies to fluctuate from one generation to the next

founder effect

few individuals isolated from a larger population and establish new, different from source

bottleneck effect

severe drop in population size, changes allele breakdown, low genetic diversity on other side of bottleneck

hybridization

mating of individuals from two species w/ incomplete reproductive barriers

hybrid zone

overlap in population ranges of different species allowing hybrids

reinforcement

hybrids less fit than parents, strengthen repro barriers

fusion

weakening of reproductive barriers, gene flow increases over time

stability

same number of hybrids produced over time