BIO E121 Lecture Notes - Lecture 8: Meiosis, Dendrobium, Speciation
Document Summary
Mechanisms that prevent members of different species from interbreeding and producing viable, fertile offspring. Prevents formation of hybrids offspring of interspecific mating. Hybrids bad for fitness takes energy to make, but generally low fitness. Barriers to reproduction: prezygotic isolating mechanisms, operate prior to zygote formation > prevent fertilization (ex. Gametes incompatible: habitat isolation, overlapping geographic range, but live/breed in different areas. > rarely interact, no opportunities to mate: temporal isolation, overlap, but breed at different times different times of year, season, day. Example: dendrobium, genus of orchids flower on different days, only open for 1 day: behavioral isolation. Example: courtship rituals females only respond to males doing the right thing: mechanical isolation, mating is attempted, but sexual structures prevent successful mating, gametic isolation, molecular or chemical differences between species egg and sperm incompatible. Example: common in aquatic organisms release gametes into water: but sometimes fertilization occurs between 2 species, postzygotic barriers, operate after fertilization occurs, reduced hybrid viability.
