Chapter 24

reproductive isolation is the existence of biological barriers that impede two species from producing viable, fertile hybrids

prezygotic and postzygotic

prezygotic barriers impede mating or hinder fertilization if mating does occur

• habitat isolation: two species don’t encounter each other because of different habitats • temporal isolation: species breed at different times, so gametes cannot mix • behavioral isolation: courtship rituals and other behaviors unique to a species are effective barriers • mechanical isolation: morphological differences, they dont fit together • gametic isolation: sperm may not be able to fertilize eggs

post-zygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult

• reduced hybrid viability: genes of the different parent species may interact and impair hybrid’s development • reduced hybrid fertility: even if hybrids are vigorous, they may be sterile (mules cant reproduce) • hybrid breakdown: some hybrids are fertile, but when they mate, offspring of next generation are feeble or sterile

speciation can occur in allopatric speciation or sympatric speciation

in allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations, they may undergo evolutionary change during separation

in sympatric speciation, speciation takes place in geographically overlapping populations

reproductive isolation must have been established

if they are reproductively compatible; cannot interbreed with other populations

polyploidy is presence of extra sets of chromosomes due to accidents during cell division, it is a common way for plants to become a different species

polyploidy is sympatric

allopatric is formation of new species from being separated sympatric is a reproductive barrier that isolates population without being separated