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Chapter 8

Chapter 8. Cell Reproduction. 8-1. Chromosomes. DNA. Long, thin molecule that stores genetic information Instructions for Life. Chromosomes. DNA coiled up This happens during cell division. Histones. Proteins that the DNA wraps around to make chromosomes. Chromatid.

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Chapter 8

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  1. Chapter 8 Cell Reproduction

  2. 8-1 Chromosomes

  3. DNA • Long, thin molecule that stores genetic information • Instructions for Life

  4. Chromosomes • DNA coiled up • This happens during cell division

  5. Histones • Proteins that the DNA wraps around to make chromosomes

  6. Chromatid • Each half of a chromosome • “sister chromatids” = chromosome

  7. Centromere • Holds chromatids together until they separate during cell division

  8. Chromatin • Less tightly coiled DNA/protein • Happens when the cell is NOT dividing so the information can be used

  9. Chromosome Numbers • Each species has its own number of chromosomes in each cell • Ex: Fruit Flies = 8 Carrot = 18 Cat = 32 Human = 46

  10. Two Types of Chromosomes • 1. Sex chromosomes • 2. autosomes

  11. Sex Chromosomes • Chromosomes that determine if an animal is a male or a female • Females = X and X • Males = X and Y

  12. Autosome • All other chromosomes that do not determine the sex of an animal • Each cell has two copies of each autosome • Example: DNA for eye color

  13. Homologous Chromosomes • The two copies of each autosome • Same size and shape • Carry genes for the same traits (for example blue eye color)

  14. Karyotype • A picture of homologous chromosomes

  15. Diploid • Cells with two sets of chromosomes

  16. Haploid • One set of chromosomes • Ex: human sperm and egg cells

  17. Chapter 8.3 Meiosis

  18. Types of Reproduction • Asexual reproduction • Produce offspring with only ONE parent • “babies” are identical to parent • Sexual reproduction • Produce offspring by meiosis and the joining of the sperm and egg • “babies” are NOT identical to parents

  19. Meiosis • New cells have half the number of chromosomes • Gametes • Reproductive cells (sperm and egg)

  20. Key Points • Meiosis must happen so when the sperm and egg join to create a new organism, it has the correct number of chromosomes. • Examples: • Human = 46 • Egg = 23 • Sperm = 23 • Egg + Sperm = baby • 23 + 23 = 46

  21. Meiosis I. (very similar to mitosis) • Prophase I. • DNA coils into chromosomes • Each chromosome lines up with its homologue (the similar chromosomes) • Synapsis: pairing of homologous chromosomes • Each pair is called a tetrad • Crossing-over: may occur where pieces of one chromosome break off and attach to the other chromosome  genetic recombination

  22. Metaphase I. • Tetrads line up along the middle of the cell

  23. Anaphase I. • Each homologous chromosome of each tetrad moves to opposite ends of the cell

  24. Telophase I. • Cell divides creating 2 new cells each with a haploid number of chromosomes (1/2 the original number of chromosomes, but 2 copies of each)

  25. Meiosis II. (DNA does NOT get copied first) • Prophase II. • Chromosomes begin to move

  26. Metaphase II. • Chromosomes move to the cell’s midline

  27. Anaphase II. • Chromatids separate and move to opposite ends of the cell

  28. Telophase II. • Four new cells form with ½ the original number of chromosomes

  29. **Meiosis occurs ONLY IN REPRODUCTIVE ORGANS. • See Figure 8-12 page 155

  30. Spermatogenesis: • Production of sperm cells • Oogenesis: • Production of egg cells

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