classnotes10 - Reproduction: Methods of reproduction: -...

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Reproduction: Methods of reproduction: - asexual. This only involves a single animal, and the genes of the offspring all come from the parent (without going through sperm/egg fusion). - sexual. Involves fusion of egg and sperm to develop a zygote. A zygote is the cell that results from fusion of egg and sperm. Asexual: - fission - the parent splits into two more or less equal halves. Each half then goes on to grow and mature. - budding - generally similar, but here the parent may bud off new individuals that are smaller than parent. This new individual may remain attached, or separate. - corals (cnidarians) - young stay attached. - hydra (also cnidarians) - young detach. - fragmentation - the body breaks into several pieces, each of which can form a new individual. [This does not include merely re-growing limbs (or tail)]. Starfish example. Some animals may reproduce both sexually and asexually. Corals again are a good example. In general, sexual reproduction is used during more stressful times, and asexual reproduction when times are good (why?). Parthenogenesis: - Egg develops without being fertilized. Resulting individual may be haploid or diploid, depending on whether or not haploid egg doubles before developing. - occurs in many animals, e.g. Rotifers, Daphnia, and whiptail lizards. Sexual reproduction - obviously, fertilization is required. Sperm must meet up with and fertilize egg. - problem for sessile organisms. How to transport sperm?? E.g., tapeworm. - one solution -> hermaphroditism. A hermaphrodite has both female and male reproductive structures. This makes it easier to find a mate. Also, since two individuals can exchange sperm, potentially twice as many offspring can be produced (though this is really a bit more complicated than that!!).
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- sequential hermaphroditism. Some fish can change sex during lifetime. This depends on whether large size may be an advantage - e.g. in some fish males defend territory, so they need to be larger. Just be aware that this exists. - methods of fertilization: - external - union of sperm and egg occurs outside the body. Typically, eggs are released by the female, then the male covers the eggs with sperm. Many animals will do this (frogs, many fish, etc.) - internal - sperm are deposited in or near the female reproductive tract, and fertilization occurs within the female reproductive tract. - note: many mechanisms are in place to insure that mating takes place only within the same species - behavior, pheromones, environmental cues - for vertebrates (and some others), we can consider the following breakdown as well: - oviparous - animal lays egg, embryo develops within egg, egg hatches. - viviparous - animal develops inside body of mother, AND gets nutrients
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This note was uploaded on 07/21/2011 for the course BIO 101 taught by Professor Staff during the Spring '08 term at Northern Virginia Community College.

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classnotes10 - Reproduction: Methods of reproduction: -...

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