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Understanding Cell Reproduction and Chromosomes

Explore the intricacies of cell division, chromosomes, DNA, and the critical process of meiosis for sexual reproduction. Learn about chromosome numbers, homologous chromosomes, sex chromosomes, and more in this informative chapter.

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Understanding Cell Reproduction and Chromosomes

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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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