Chapter 44 Principles of Reproduction and Development

Chapter 44 Principles of Reproduction and Development -...

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Chapter 44 Principles of Reproduction and Development I. The Beginning: Reproductive Modes A. There are two basic types of animal reproduction: 1 Asexual reproduction by budding (example: sponge) or fission (example: flatworm) results in offspring identical to the parents; this is a useful strategy in stable environments. 2 Sexual reproduction permits adaption through variation but is biologically costly because the sexes are separate; animals must produce gametes and must find each other (usually) for fertilization to occur. B. Difficulties must be overcome by animals that achieve reproductive success with separate sexes. 1 Reproductive timing must allow for male and female gametes to be available at nearly the same time. a. Sensory structures and hormonal controls must be precise in both parents. b. Seasonal cues and behavioral patterns must evoke a suitable response in both sexes. 2 Fertilization also comes at a cost with separate sexes. a. External fertilization in water requires the production of large numbers of gametes. b. Internal fertilization requires an investment in elaborate reproductive organs, including the penis, to transfer sperm to the female. 3 Energy is set aside for nourishing some number of offspring. a. Those eggs with little yolk must develop larval stages quickly. b. Others, such as birds, have adequate food reserves for a more lengthy development within the shell. c. Some eggs, such as those of humans, have no yolk; the embryo must be nourished with energy molecules drawn from the mother. II. Stages of Development A. Gamete formation: eggs or sperm form and mature within the parents. B. Fertilization begins when a sperm penetrates an egg and is completed when the sperm nucleus fuses with the egg nucleus, resulting in formation of the zygote. C. Repeated mitotic divisions—cleavage—convert the zygote to a blastula; cell numbers increase but not cell size. D. Gastrulation results in three germ layers, or tissues: 1 Endoderm is the inner layer; it gives rise to the gut and organs derived from it. 2 Mesoderm is the middle layer; muscle, organs of circulation, reproduction, excretion, and skeleton are derived from it. 3 Ectoderm is the outer layer; it gives rise to the nervous system and the outer layers of the integument.
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.

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Chapter 44 Principles of Reproduction and Development -...

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