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Biological Sciences
Mark Fitzpatrick

Speciation and Reproductive isolation mechanisms Species: group of individuals who are able to mate amongst themselves to make healthy offsprings Exceptions: Horses and donkeys mate to make mules -Hooded crow and carrion crows can make hybrids, but are geographically separated Reproductive Isolation Mechanisms: factors that does not allow for successful reproduction Pre zygotic Barriers: prior to when a zygote is formed -Prevention of Mating: doesn’t allow for having sex -Behavioral Isolation: each species may use different signals or behaviors to attract mates. Sometimes they don’t work or are incompatible. -Birds and frogs sing a song -Temporal Isolation: mating at the wrong time cannot allow them to mate even though they could be in the same habitat. -Flower mating seasons -Ecological/Habitat Isolation: species occupy different habitats within the same area wherethey’re separated and cannot mate -Northwest Garter snakes prefer meadows while common garter snakes are in water all the time Prevention of fertilizing: doesn’t allow for fertilization -Mechanical Isolation: Different species don’t mate because their genitals aren’t compatible for mating -Genitals of damsel flies are different from other flies and can only mate with their own species -Gametic Isolation: If gametes from different species do not meet, barriers preventing sperm and eggs from forming a zygote. -Sperm might not survive in female, or molecular markers on eggs signal sperms that this isn’t the right egg, and will ignore it Post Zygotic Barriers: doesn’t allow for successful growth of the hybrid (refers to offspring from mating 2 species) -Reduction of Hybrid viability: Fetus forms after fertilization, but followed by spontaneous abortion due to genetic incompatibility. -lethal alleles terminates the process -chromosome number mismatches, first stage of mitosis terminates -Reduced zygotic barriers: Hybrid offspring could become sterile. Problem because chromosome number during mating because parental chromosomes differ from other species or parental species. -Donkey and horse’s hybrid is sterile -Hybrid Breakdown: F1 hybrids may work, but F2 hybrids are often always ste
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