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Chapter 10 Sexual Reproduction & Genetics

Chapter 10 Sexual Reproduction & Genetics. Part 1: Meiosis. Concepts for Review. Chromatin is the relaxed form of DNA Chromosome is the coiled form of DNA Sister chromatids are identical copies of DNA (after S-phase/replication). Key Terms .

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Chapter 10 Sexual Reproduction & Genetics

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  1. Chapter 10 Sexual Reproduction & Genetics Part 1: Meiosis

  2. Concepts for Review • Chromatin is the relaxed form of DNA • Chromosome is the coiled form of DNA • Sister chromatids are identical copies of DNA (after S-phase/replication)

  3. Key Terms • Homologous chromosomes are chromosomes that make up a pair, one from each parent • Not necessarily identical but… • Are the same length • Have the same genes

  4. Key Terms • Diploid refers to complete chromosome sets in a cell (or 2N) • N= the number of chromosomes in a gamete (sex cell) • N chromosomes from the female parent + N chromosomes from the male parent= 2N • For humans, 2N = 46

  5. Key Terms • Haploid refers to single chromosomes in a cell (or N) • One-half of the 2N set (the maternal N or the paternal N) • Gametes (i.e. sperm, egg sex cells) are haploid cells • For humans, N = 23

  6. Bottom Line • diploid means that there are the full number of chromosomes where as haploid means that there are half the number of chromosomes.

  7. Key Terms • Meiosis is a type of cell division that reduces the number of chromosomes • Forms gametes (i.e. sex cells) • Occurs in the reproductive structures of organisms that reproduce sexually • Occurs in 2 consecutive cell divisions: meiosis I and meiosis II

  8. Before meiosis Interphase occurs…. • Replication of DNA occurs. • Chromosomes Condense Sounds familiar right???

  9. Reducing 2N cells to… Meiosis I: “Reduction Division” N cells

  10. PROPHASE I • Homologous chromosomes pair up • Crossing over occurs • Nuclear envelope breaks down • Spindles form

  11. Crossing Over • Chromosomal segments (genetic information) are exchanged between a pair of homologous chromosomes

  12. METAPHASE I • Spindle fibers attach to the centromeres • Homologous Chromosomes Line up at the equator

  13. ANAPHASE I • Homologous chromosomes separate and move to the opposite poles of the cell

  14. TELOPHASE I • The cell divides • The result is two daughter cells. • Each daughter cell is haploid. • The daughter cells are not genetically identical **During Telophase I Cytokinesis occurs at the same time!!**

  15. Meiosis II: “Mitotic Division” Separating sister chromatids

  16. Nucleus breaks up • Spindles form and attach to centromere

  17. Sister chromatids randomly align at middle of cell

  18. Sister chromatids separate • Chromosomes move to opposite poles of cell

  19. Cells divide • 4 haploid daughter cells result • Each cell is genetically different

  20. Summary of Key Concepts • Chromosomes contain genes (humans have 46 chromosomes or 23 homologous pair) • Homologous chromosomes may contain different forms of the same genes • Meiosis reduces chromosome # by ½ and results in sex cells (gametes) • Crossing-over increasing genetic variation Click here for detailed animation of meiosis

  21. which set of chromatids illustrates the result of a single crossover of the homologous chromosomes?

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