Chpt.50-Sex and Reproduction

Chpt.50-Sex and Reproduction - Chapter 50 Sex and...

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Chapter 50 – Sex and Reproduction The theme of this chapter is obvious and doesn’t need amplification. Our main focus will be on Chapter 50, the types of reproduction, the reproductive systems of male and females, birth control, and sexually transmitted diseases or infections. We will delve into Chapter 51 as appropriate. The Concept Outline (P. 1061) and the Concept Review (P.1079) provide excellent coverage of the subject. We have not always known how human conception occurred. Our understanding of sexual gratification has a long and entangled history, but the basics of human creation was a mystery until recently. The following information is not in your textbook, but it is important. There is a history about a perceived human being called homunculus and this individual is the center piece for our early ideas about human conception. At about the time the microscope was invented, scientists believed they could see a small human in the sperm cell (or egg). Therefore, there were two camps: the spermatists and the oovists . Some scientists, those mathematically inclined, calculated how many smaller humans the microscopic human could have, and therefore when the end of the human species would occur! The story of “Preformation” is the Theory of Epigenesis . This theory goes back a long way - ~ 2,000 years, to Aristotle who proposed it. We assume our understanding is more accurate at the present time. Types of Reproduction: Asexual Reproduction : binary fission, budding, and parthenogenesis. Sexual Reproduction : Gametogenesis; dioecious vs monoecious vs hermaphrodites. Animals that practice sexual reproduction do not exhibit “Alternation of Generations” as seen in plants, BECAUSE the haploid reproductive cells that result from meiosis (gametes) do not divide by mitosis before fusing to form a 2N zygote (Chpt. 31, P. 619). Advantages of metamorphosis: Different environments – think about it. External Fertilization and the different types of Internal Fertilization: Reproduction in vertebrates evolved in the marine environment before vertebrates colonized land. It began with the fishes. Most marine bony fish practice external fertilization where the female releases eggs into the environment and males release sperm into the same area. The sperm find the eggs, fertilization occurs, a zygote is formed, and most die. Cartilagenous fish, such as sharks, have more advanced fertilization. Once vertebrates began to live on land, the goal was to escape having to return to water to reproduce. Most amphibians (Fig. 50.5) never evolved internal fertilization methods and hence were never “true” land animals. The vertebrates that did evolve into “true” land animals developed three strategies for embryonic development: oviparity , ovoviviparity , viviparity (P. 1064). These terms are very important in your education – memorize them well. They are the noun forms (I think I am correct in saying they are nouns). The adjective forms are: oviparous , ovoviviparous
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This note was uploaded on 03/31/2008 for the course BIOL 1106 taught by Professor Georgesimmons during the Spring '08 term at Virginia Tech.

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Chpt.50-Sex and Reproduction - Chapter 50 Sex and...

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