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Lecture Notes Chapter 46

Lecture Notes Chapter 46 - Chapter 46 Animal Reproduction A...

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Chapter 46 Animal Reproduction A population transcends finite life spans only by reproduction Both asexual and sexual reproduction occur in the animal kingdom Asexual reproduction is the creation of new individuals whose genes all come from one parent Sexual reproduction is the creation of offspring by the fusion of male and female gametes to form a zygote o The female gamete is the egg o The male gamete is the sperm Male gametogenesis: Spermatogonium o stem cell, produces more spermatogonia Primary spermatocyte o 2N, undergoes meiosis I Secondary spermatocyte o 1 N, undergoes meiosis II to generate: Spermatids o Precursors which differentiate to become: Mature sperm Female gametogenesis: Oogonium Stem cell, do not divide in mature humans Primary oocyte o 2N, undergoes meiosis I Secondary oocyte + polar body o 1 N, undergoes meiosis II to generate: Ovum Mature egg cell Mechanisms of Asexual Reproduction Many invertebrates reproduce asexually by - fission : the separation of a parent into two or more individuals of approximately the same size o Single-celled protozoa, lower worms, cnidaria budding in which two new individuals arise from outgrowths of existing ones o cnidaria, corals fragmentation , which is the breaking of the body into several pieces, some or all of which develop into complete adults o Must be accompanied by regeneration, the re-growth of lost body parts 1
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Reproductive Cycles and Patterns Most animals exhibit cycles in reproductive activity Often related to changing seasons o Reproductive cycles are controlled by hormones and environmental cues Animals may reproduce exclusively asexually or sexually Or they may alternate between the two Some animals reproduce by parthenogenesis A process in which an egg develops without being fertilized Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizards reproduce exclusively by a complex form of parthenogenesis Sexual reproduction presents a special problem for certain organisms that seldom encounter a mate One solution to this problem is hermaphroditism o each individual has both male and female reproductive systems o sequential hermaphroditism - an individual reverses its sex during its lifetime Fertilization depends on mechanisms that help sperm meet eggs of the same species The mechanisms of fertilization, the union of egg and sperm play an important part in sexual reproduction 1. External fertilization: eggs shed by the female are fertilized by sperm in the external environment fertilization requires critical timing often mediated by environmental cues, pheromones, and/or courtship behavior 2. Internal fertilization: sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract Requires important behavioral interactions between male and female animals Requires compatible copulatory organs Ensuring the Survival of Offspring
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Lecture Notes Chapter 46 - Chapter 46 Animal Reproduction A...

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