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CHAPTER 1 3 MEIOSIS AND SEXUAL LIFE CYCLES OUTLINE I. An Introduction to Heredity A. Offspring acquire genes from parents by inheriting chromosomes B. Like begets like, more or less: a comparison of asexual versus sexual reproduction II. The Role of Meiosis in Sexual Life Cycles A. Fertilization and meiosis alternate in sexual life cycles B. Meiosis reduces chromosome number from diploid to haploid: a closer look III. Origins of Genetic Variation A. Sexual life cycles produce genetic variation among offspring B. Evolutionary adaptation depends on a population’s genetic variation OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. Explain why organisms only reproduce their own kind, and why offspring more closely resemble their parents than unrelated individuals of the same species. 2. Explain what makes heredity possible. 3. Distinguish between asexual and sexual reproduction. 4. Diagram the human life cycle and indicate where in the human body that mitosis and meiosis occur; which cells are the result of meiosis and mitosis; and which cells are haploid. 5. Distinguish among the life cycle patterns of animals, fungi, and plants. 6. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase. 7. Recognize the phases of meiosis from diagrams or micrographs. 9. Describe the process of synapsis during prophase I, and explain how genetic recombination occurs. 10. Describe key differences between mitosis and meiosis; explain how the end result of meiosis differs from that of mitosis. 11. Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms. 12. Explain why inheritable variation was crucial to Darwin's theory of evolution. 13. List the sources of genetic variation. 168 Unit III Genetics KEY TERMS heredity karyotype zygote meiosis II variation homologous diploid cells synapsis genetics chromosomes meiosis tetrad gene sex chromosomes alternation of chiasmata asexual reproduction autosome generations chiasma clone gamete sporophyte crossing over sexual reproduction haploid cell spores life cycle fertilization gametophyte somatic cell syngamy meiosis I LECTURE NOTES Reproduction is an emergent property associated with life. The fact that organisms reproduce their own kind is a consequence of heredity. Heredity = Continuity of biological traits from one generation to the next • Results from the transmission of hereditary units, or genes , from parents to offspring.
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• Because they share similar genes, offspring more closely resemble their parents or close relatives than unrelated individuals of the same species. Variation
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