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Sexual Reproduction

Sexual Reproduction. Chapter 9 (p127-140). Objectives. Describe the major events in meiosis Compare and contrast mitosis and meiosis Predict the consequences of errors in meiosis. Mini case study: Down syndrome. Down syndrome occurs in 1 in 800 births (mother < 40 years old)

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Sexual Reproduction

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  1. Sexual Reproduction Chapter 9 (p127-140)

  2. Objectives • Describe the major events in meiosis • Compare and contrast mitosis and meiosis • Predict the consequences of errors in meiosis

  3. Mini case study: Down syndrome • Down syndrome occurs in 1 in 800 births (mother < 40 years old) • Variety of physical symptoms, mental retardation • ____________ • Extra copy of chromosome 21 • How could cells get an extra copy of one chromosome? http://www.ndss.org/index.php?option=com_content&task=section&id=31&Itemid=194 http://www.nlm.nih.gov/medlineplus/ency/article/000997.htm

  4. Sexual reproduction • Sexual reproductioninvolves fusion of gametes from two parents • Offspring have a combination of chromosomes from each parent • Formation of gametes requires a different form of cell division called ____________ • ________________ of total # of chromosomes from parent cell to daughter cell • Separation of _______________________

  5. Homologous chromosomes • Chromosomes exist in PAIRS • Homologous = same size, shape, and centromere location • Humans have _____ homologous pairs of chromosomes

  6. Homologous chromosomes

  7. Mini case study: Down syndrome

  8. Homologous chromosomes • Homologous chromosomes carry the same genes • BUT, they can carry different versions of a gene • Different versions of the same gene are called ________________

  9. Homologous chromosomes may contain different alleles Chromosome 1 (paternal) Chromosome 1 (maternal)

  10. Homologous chromosomes • Somatic cells have homologous pairs of chromosomes (2 complete sets) • _________________ • Gametes have only one set of chromosomes • _________________ http://www.nationalgeographic.com/books/9810/journey.html

  11. The human life cycle

  12. Overview of meiosis • Meiosis begins with one diploid cell and results in ____________________________ • Chromosomes replicate, just like in mitosis • This is followed by TWO rounds of division!

  13. Division I Division II Overview of meiosis Parent cell before DNA replication

  14. Overview of meiosis

  15. Phases of meiosis • The phases of meiosis are very similar to phases of mitosis – Prophase – Metaphase – Anaphase – Telophase See meiosis animations on ARIS

  16. Meiosis compared to mitosis

  17. Mini case study: Down syndrome • Down syndrome results from nondisjunction http://www.ndss.org/index.php?option=com_content&task=section&id=31&Itemid=194

  18. Mistakes in meiosis

  19. Meiosis leads to genetic diversity in offspring • Offspring have ________ number of chromosomes as parents • Exchange of small pieces of chromosomes (____________________) can occur during the first division • New combinations of alleles occur in offspring

  20. + + OR Meiosis leads to genetic diversity in offspring

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