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Transcript
EVOLUTION Date: CH 13: How Populations Evolve (p.256) Darwinism Evolution: inherited Δ in organisms over time Theory: well-supported, well-tested explanation for natural phenomena On the Origin of Species (1859) revealed Darwin’s theory of natural selection as the mechanism for evolution o Conflicted w/ hypothesis of Jean-Baptiste Lamarck that said use & disuse leads to acquired characteristics that can be inherited by offspring o Observations: there is variation in nature, much of which is heritable (genetic) the size of a pop. tends to remain stable Resources become limited as pop. density ↑’s o Inferences: There is a struggle for existence among members of a pop. Survival depends on inherited characteristics called adaptations that ↑ fitness (the ability to survive & reproduce) in a SPECIFIC env Adaptations will become more common over time Date: Natural Selection (survival of the fittest) – individuals better suited to their env. survive & reproduce most successfully o Dependent on genetic variation & specific env./habitat o Can only edit existing characteristics; does not create new ones Ex: wings evolved from appendages that were not used for flying; our knees & backs were derived from 4-legged animals, & this partly explains why people frequently have knee & back problems o Does not lead to “perfect” individuals o It is situational Adaptations in 1 env. may be useless or harmful in another env. o Populations evolve, not individuals Species (spp): group of individuals (pop.) that interbreed & produce fertile offspring Date: Evidence of Evolution (p.260) A. Fossils: preserved remains of ancient organisms o The Fossil Record is incomplete b/c most organisms do not form fossils & they are hard to find o Age is determined by: Relative dating - compare placement w/ fossils in other rock layers Radiometric dating - use of isotope half-lives to determine absolute age of rocks B. Biogeography o Spp tend to be more closely related to other spp from the same area than to spp in dif areas w/similar conditions Ex: Darwin noticed similarities b/w organisms on the Galapagos & S. America that were dif from organisms living in similar climates on other continents C. Comparative Anatomy: shows evolution is a remodeling process that alters existing structures o Homologous structures: have dif. fxns but similar structure Evidence that spp share a common ancestor o Analogous structures: same fxn & form; evolved independently from dif ancestors Shows that adaptations develop in certain env. Vestigial structures: functioned in ancestors but not in modern spp Unaffected by NS because they do not HARM the organism Ex: whale fossils w/ pelvic bones o Comparative embryology Embryos look very similar & start to differ as they develop Suggests spp descended from a common ancestor D. Molecular Biology o Universal genetic code (DNA) o Certain genes are conserved across dif spp Ex: developmental genes, hemoglobin in vertebrates o More differences in DNA or AA sequence of protein indicates more distantly related spp E. Observational Evidence o Shifts in frequency of finch beak sizes in response to drought o Antibiotic resistance in bacteria o Insecticide resistance in insects o Herbicides resistance in plants o Date: Microevolution (p.268) Gene pool: total # of genes in a pop. Microevolution: Δ w/in a spp that lead to Δ’s in allele frequencies o Greater variation ↑’s chances of some members of a spp surviving Δ’s in the env Macroevolution: Δ that occurs as new spp evolve o Results from the accumulation of small Δ’s over time in separate pop. Hardy-Weinberg equilibrium predicts the gene pool of a pop that is NOT evolving o 5 standards of HW: 1. Infinite pop size 2. Mating is random 3. No mutation 4. No migration in or out 5. No selection (all genotypes confer equal fitness) o HW equilibrium rarely occurs in nature but can be used to predict allele frequencies in a pop & analyze the causes of evolution o HW equations: p+q=1 p2 + 2pq + q2 = 1 - p = frequency of dominant allele - q = frequency of recessive allele - p2 = frequency of homozygous dominant - 2pq = frequency of heterozygous - q2 = frequency of homozygous recessive Date: Causes of Microevolution (p.270) A. Natural selection B. Genetic drift: Δ in allele frequencies due to chance – can lead to ↓ in genetic variation o More of 1 allele might be inherited than another o Bottleneck effect: genetic drift from a drastic ↓ in pop size due to an environmental event o Founder effect: genetic drift from a small # of ind. colonizing a new area C. Gene Flow: migration of ind. or gametes b/w pop. o May ↓ genetic differences in populations D. Mutation: random Δ in DNA produces a new allele o Rare b/c most mutations have no effect (silent) or are harmful/lethal (deleterious) Date: Types of Selection (p.276) Stabilizing selection favors avg. ind. o Occurs in stable environments o ↓’s variation o Ex: human birth weight Directional selection favors 1 phenotypic extreme o Most common during environmental Δ’s or when spp migrate to a new habitat o Ex: selection of longer horns in Texas longhorns Disruptive/diversifying selection favors both phenotypic extremes o Common in variable env. o Ex: beak size in finches Sexual selection: mates are chosen based on phenotype o May lead to sexual dimorphism: males & females look dif Traits often indicate high fitness - Ex: peacock w/ big, colorful feathers that survives predators despite attracting them Artificial Selection: selective breeding of plants & animals by humans Date: Speciation (p.284) Formation of new spp is dependent on reproductive isolation: 2 pops stop interbreeding May result from: o Temporal isolation – 2 pop breed at dif times o Habitat isolation – geographic barriers separate 2 pop o Behavioral isolation – 2 pop have dif reproductive strategies Ex: mating behaviors