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Sexual Reproduction and Genetics

Sexual Reproduction and Genetics. Chapter 10. 10.1: Meiosis. MAIN IDEA: Meiosis produces haploid gametes. In Our Body Cells:. Each chromosome has a matching pair - homologous pairs One chromosome from each pair came from mother, other from father

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Sexual Reproduction and Genetics

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  1. Sexual Reproduction and Genetics Chapter 10

  2. 10.1: Meiosis MAIN IDEA: Meiosis produces haploid gametes.

  3. In Our Body Cells: • Each chromosome has a matching pair - homologous pairs • One chromosome from each pair came from mother, other from father • Homologous chromosomes - code for the same type of traits, but don’t have the exact same information

  4. Human Chromosomes

  5. Humans • Have 23 pairs of chromosomes (46 total) • Each chromosome has about 1500 genes • Genetic info passed from parents to children in sexual reproduction

  6. 1. Asexual Single parent Offspring- genetically identical to parent No sex cells 2. Sexual 2 parents Offspring - genetically different from parents – variation Involves sex cells Types of Reproduction

  7. Body Cells vs. Sex Cells • Body (somatic) cells • Diploid - contain both chromosomes of each pair • Represented by 2n • Sex cells (gametes) • Haploid - Contain half the number of chromosomes; only one of each pair • Represented by n

  8. Haploid and Diploid • If corn body cells have 20 chromosomes, how many are in the gametes? • If an organism has a haploid number of 18, what is the diploid number? • n= 24. Is this the haploid or diploid? Is this the number of chromosomes in the gametes or body cells?

  9. Meiosis • Special type of cell division that forms gametes – occurs in reproductive parts • Meiosis called reduction division – reduces # of chromosomes in half • Fertilization – 2 gametes combine – zygote cells are diploid • Sexual reproduction is a cycle

  10. Meiosis • Interphase (same as before) • 2 divisions: • Meiosis I • Meiosis II • How many cells will result? • How many cells resulted from mitosis?

  11. Phases of Meiosis • Meiosis I • Prophase I, metaphase I, anaphase I, telophase I • Meiosis II • Prophase II, metaphase II, anaphase II, telophase II

  12. What happens in each phase?

  13. Prophase I (like mitosis) • Chromosomes become visible; sister chromatids join at centromeres • Nuclear membrane disappears; Spindle fibers start to form

  14. Prophase I (only meiosis) • 2 matching homologous pairs (one from father, one from mother) join together – synapsis • Crossing over occurs - piece of one chromosome is exchanged with piece of another

  15. chromatid centromere

  16. Crossing Over

  17. Prophase I

  18. Metaphase I • Matching homologous pairs (tetrads) line up across equator of cell • Line up randomly • Spindle fibers attach to centromeres of homologous pairs

  19. Anaphase I • Each pair of matched chromosome from the homologous pairs move to opposite ends of the cell • Reduced from 2n to n

  20. Telophase I • Matching pairs have moved to opposite ends; cytokinesis occurs to make 2 cells

  21. After Meiosis I… • Cells have half the number of chromosomes as original cell, but in matching pairs

  22. DO NOW • What is the end result of meiosis? • Why is meiosis called a “reduction division”, and why is it important? • What is a homologous pair of chromosomes? • If a cell contains 54 chromosomes before meiosis, how many are in each cell after meiosis?

  23. Meiosis II • Similar to mitosis • NOT another interphase • Prophase II – chromosome pairs begin moving toward equator and spindle fibers form • Metaphase II – chromosome pairs line up across equator; spindle fibers attach to each chromatid at centromere

  24. Meiosis II Prophase II Metaphase II

  25. Meiosis II cont’d • Anaphase II – pairs of chromosomes are separated, and move along spindle toward poles of cell • Telophase II – chromosomes are at opposite ends of cell, cytokinesis occurs • After Meiosis II – 4 haploid daughter cells

  26. Meiosis II cont’d Anaphase II Telophase II 4 cells

  27. Answer the Following: • How does the chromosome # change with each cycle of mitosis and fertilization? • What must occur to keep the chromosome number constant when fertilization occurs?

  28. DO NOW • What is the end result of meiosis? • What is a homologous chromosome pair? • Why is it important that meiosis is a “reduction” division?

  29. Genetic Variation • During prophase I, crossing over can occur • Because homologous pairs are randomly separated, different gametes are formed • When chromosomes recombine during fertilization, new combination of chromosomes results

  30. Genetic Variation

  31. Checkpoint • How is sexual reproduction an advantage to a species? • Explain 2 reasons why you do not look exactly like either of your parents.

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