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The Origen of Species Ch 24 Macroevolution • Evolution above the species level that produces novelties like vertebrae or feathers and contributes to speciation – Speciation- the process by which new species arise – Species: capable of reproducing and making fertile offspring Reproductive Isolation • Prevents different species from making fertile offspring. • May be “prezygotic” or “postzygotic” Prezygotic barriers • • • • • 1. Habitat isolation 2. Behavioral Isolation 3. Temporal(time) isolation 4. Mechanical isolation 5. Gametic isolation Postzygotic barriers • 1. Reduced hybrid viability- zygote doesn’t develop • 2. Reduced hybrid fertility- offspring is sterile • 3. Hybrid breakdown- fertile hybrids mate but their offspring are weak/sterile Allopatric Speciation • “Different country” speciation due to geographic separation – Mountains forming, rivers separating, continental drift,etc Sympatric Speciation • “Same country” speciationSome barrier prevents mating (Temporal, behavioral…) – Common in plants that easily become polyploid instead of diploid --may result from Habitat differentiation and sexual selection Adaptive radiation (divergent evolution) • -many species arise from a common ancestor which moved into a new area or niche Rates of Speciation • Gradualism- gradual accumulation of adaptations • Punctuated equilibrium- stable periods with occasional bursts of rapid changes in the fossil record Evolution of Genes that Control Development • “Evo-devo” is the branch of study where evolution and developmental biology meet. -Slight changes can make major differences in morphology difference between species. Homeotic Genes • Master control genes that determine the location and organization of body parts – Hox genes determine positional information in animal embryos that prompt cells to develop structures in a particular place – Changes can create drastic morphological effects