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SPECIATION CH. 16-3 PP. 326-330 FORMING A NEW SPECIES Speciation: forming a new species FORMING A NEW SPECIES Speciation: forming a new species Species: a group of organisms that can mate and produce fertile offspring FORMING A NEW SPECIES Speciation: forming a new species Species: a group of organisms that can mate and produce fertile offspring 1. same number of chromosomes 2. similar morphology (body structure) DISRUPTIVE SELECTION Divergent evolution that most likely results in two new species MECHANISMS • Allopatric speciation caused by geographic isolation MECHANISMS • Allopatric speciation caused by geographic isolation • physical separation of organisms (mountain, river forms etc) MECHANISMS CONT. • Sympatric Speciation due to reproductive isolation MECHANISMS CONT. • Sympatric Speciation due to reproductive isolation • Live in the same area • Barriers to successful breeding MECHANISMS CONT. Two types of Sympatric Speciation Barriers • Prezygotic: before fertilization (i.e breeding times, mating calls etc.) MECHANISMS CONT. Two types of Sympatric Speciation Barriers • Prezygotic: before fertilization (i.e breeding times, mating calls etc.) • Postzygotic: after fertilizationinfertile offspring (chromosome # doesn’t add up) RATES OF SPECIATION • Gradualism: slow divergence (small changes) • Punctuated equilibrium: sudden shift in form (irregular) PRE OR POSTZYGOTIC? • offspring die young when two species of salamanders mate – they do not make it to maturity PRE OR POSTZYGOTIC? • Two different species of birds have different mating calls so they cannot recognize each other as mates PRE OR POSTZYGOTIC? • garter snakes that live in water and one on land cannot mate although they live in the same geographic area PRE OR POSTZYGOTIC? • mules are produced by mating a horse and a donkey, but mules are sterile and cannot breed PRE OR POSTZYGOTIC? • if gametes of red and purple sea urchins do not fuse, there will be no zygote produced PRE OR POSTZYGOTIC? • although some strains of cultivated rice can be cross-mated, after a few generations, sterile offspring are created