Chapt 46 - CHAPTER 46 ANIMAL REPRODUCTION Overview of...

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CHAPTER 46 - ANIMAL REPRODUCTION Overview of Animal Reproduction 1. Both asexual and sexual reproduction occur in the animal kingdom Asexual reproduction involves the formation of individuals whose genes all come from one 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 zygote . Ovum : female gamete - usually large and nonmotile. Spermatozooan : male gamete - usually small and motile. Sexual reproduction increases genetic variation among offspring. 2. Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly Invertebrates: Fission : asexual reproduction in which a parent separates into two or more approximately equal-sized individuals. Budding : asexual reproduction in which new individuals split off from existing ones. Gemmules of sponges are an example of a type of asexual reproduction that involves the release of specialized cells that can grow into new individuals. Fragmentation : the breaking of the body into several pieces, some or all of which develop into complete adults. Requires regeneration of lost body parts. Advantages of asexual reproduction: Can reproduce without needing to find a mate. Can have numerous offspring in a short period of time. In stable environments, allows for the perpetuation of successful genotypes. 3. Reproductive cycles and patterns vary extensively among mammals Reproductive cycles are controlled by both environmental and hormonal cues. Animals may be solely asexual or sexual. Or they may alternate between the two modes depending on environmental conditions. Daphnia reproduce by parthenogenesis under favorable conditions and sexually during times of environmental stress. Parthenogenesis is the process by which an unfertilized egg develops into an (often) haploid adult. Parthenogenesis plays a role in the social organization of species of bees, wasps, and ants. Male honeybees are haploid and female honeybees are diploid. Several genera of fishes, amphibians, and lizards reproduce by a form of parthenogenesis that produces diploid zygotes. Sexual reproduction presents a problem for sessile or burrowing animals or parasites who may have difficulty encountering a member of the opposite sex. Hermaphroditism : one individual is functional as both a male and a female.
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Some self-fertilize. Most mate with another member of the same species. Each individual receives and donates sperm. Results in twice as many offspring as would occur if only one set of eggs were fertilized. Sequential hermaphroditism : an individual reverses its sex during its lifetime. Protogynous
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Chapt 46 - CHAPTER 46 ANIMAL REPRODUCTION Overview of...

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