Biology Chapter 46

Biology Chapter 46 - Chapter 46 Animal Reproduction Concept...

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Chapter 46 Animal Reproduction Concept 46.1 Both asexual and sexual reproduction occur in the animal kingdom Asexual reproduction involves the formation of individuals whose genes come from a single parent. ° There is no fusion of sperm and egg. Sexual reproduction is the formation of offspring by the fusion of haploid gametes to form a diploid zygote. ° The female gamete, the unfertilized egg, or ovum, is usually large and nonmotile. ° The male gamete is the sperm, which is usually small and motile. ° Sexual reproduction increases genetic variation among offspring by generating unique combinations of genes inherited from two parents. Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly. Many invertebrates can reproduce asexually by fission, in which a parent separates into two or more approximately equal-sized individuals. ° Budding is also common among invertebrates. This is a form of asexual reproduction in which new individuals split off from existing ones. ° In fragmentation, the body breaks into several pieces, some or all of which develop into complete adults. Reproducing in this way requires regeneration of lost body parts. Asexual reproduction has a number of advantages. ° It allows isolated animals to reproduce without needing to find a mate. ° It can create numerous offspring in a short period of time. ° In stable environments, it allows for the perpetuation of successful genotypes. Reproductive cycles and patterns vary extensively among mammals. Reproductive cycles are controlled by a combination of environmental and hormonal cues. Parthenogenesis is the process by which an unfertilized egg develops without being fertilized. ° Parthenogenesis plays a role in the social organization of some bees, wasps, and ants. Sexual reproduction presents a problem for burrowing animals or parasites that may have difficulty encountering a member of the opposite sex. ° One solution is hermaphroditism, in which one individual functions as both a male and a female. Some hermaphrodites can self-fertilize, but most mate with another member of the same species. i In such matings, each individual receives and donates sperm. i This results in twice as many offspring as would be produced if only one set of eggs were fertilized. ° In sequential hermaphroditism, an individual reverses its sex during its lifetime. of fertilization , the union of sperm and egg, play an important part in sexual reproduction. In external fertilization, eggs are released by the female into a wet environment, where they are fertilized by the Concept 46.2 Fertilization depends on mechanisms that help sperm meet eggs of the same species ° The mechanisms male. ° In species with
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Biology Chapter 46 - Chapter 46 Animal Reproduction Concept...

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