24.1 & 24.2 Macroevolution.notebook

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Ch. 24 Macroevolution 1. the broad pattern of evolution above the species level2. ex. origin of new groups of organisms through a series of speciation events

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24.1 Biological Species are reproductively isolatedA. Speciation

1. Process by which one species splits into 2 or more sp.2. Biological Species Concept

a. able to interbreed in nature and produce viable, fertile offspring

3. Key to new species: Reproductive Isolationa. barriers that stop members of 2 species from interbreedingb. 2 groups

i. Prezygotic barriers - block fertilization from occurringii. Postzygotic- may contribute to reproductive isolation after the hybrid zygote is formed

24.1 & 24.2 Macroevolution.notebook

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2 species that occupy diff. habitats within the same area may encounter each other rarely

sp. that breed at diff. times

differences in courtship behaviors

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mating is attempted, but morphological differences prevent success

sperm of 1 sp. can't fertilize the eggs of another species

24.1 & 24.2 Macroevolution.notebook

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the genes of diff. parent sp. may interact in ways that impair the hybrid's development/survival

the hybrids are infertile so cannot produce offspring

some 1st generation hybrids are fertile, but when they mate with one another or with either parent sp., the next generation's offspring are sterile

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24.2 Speciation with & without geographic separationA. Allopatric Speciation

1. Gene flow is interrupted when a pop. is divided into geographically isolated subpopulations

2. Once geographic separation occurs, the separated gene pools may diverge

3. Example: Adaptive radiationa. many new sp. evolve from a single ancestral sp.b. members of sp. become adapted to diff. environmentsc. ex. Darwin's finches

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B. Sympatric Speciation1. Speciation occurs in pops. that live in the same geographic area2. Gene flow is reduced by such factors as

a. polyploidyi. accident during cell division that results in extra chromosomesii. occurs in plants, but rarely

b. habitat differentiationi. genetic factors allow a subpop. to exploit a habitat or resource not used by the parent pop.

c. sexual selectioni. male breeding coloration separating 2 pops. if they adapt to diff. food sources resulting in genetic divergence

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The 2 Main Modes of Speciation

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