1. Genetic Isolation

2. What prevents members of different species from successfully interbreeding? • There are two isolating mechanisms: • 1. Pre-zygotic Barriers • 2. Post-zygotic Barriers

3. Pre-Zygotic Barriers • 1. Prevention of Mating • A) Habitat Isolation • Live in different habitats so species do not encounter each other • Eg. Lions and tigers

4. B) Temporal Isolation • Breeding times are different • Day vs. night, fall vs. spring • Eg. Two species of frogs live in the same field by don’t interbreed because breed in different months

5. C) Behavioural Isolation • Mating displays of different species don’t attract each other • Female species usually pay more attention to mating displays because they put more energy into their offspring and want to make sure they mate with the same species • Eg. Birds mating dances

7. 2. Prevention of Fertilization • A) Mechanical Isolation • Different species try to mate, but are anatomically incompatible • B) Gametic Isolation • Receptor molecules on the surface of ova recognize complementary molecules on sperm cells • Different species may have different receptors • Enzymes found in sperm only allowed in nucleus of ovum IF they are specific to the species

8. Post-Zygotic Barriers • A zygote forms, but these barriers prevent zygotes or resulting offspring from maturing and/or reproducing • 1. Zygote Mortality • Zygote does not develop or survive to birth • Eg. Spontaneous abortion, miscarriage

9. 2. Hybrid Inviability • Birth occurs in some cases, but offspring die before reaching adulthood • Low survival rate • Therefore, hybrids have low fitness • 3. Hybrid Infertility • Offspring survive to adulthood, but are infertile • Eg. Female horse cross with a make donkey = mule