1. Chapter 5.3 Meiosis

2. Chromosomes –Contain instructions for traits –Found on Genes Segments of DNA Code for specific proteins –46 found in the human cells 23 from each parent Chromosomes and Chromosome Number

3. Chromosomes and Chromosome Number

4. Homologous Chromosomes –Have same length –Carry same genes Hair color, eye color, height, etc. –23 homologous pairs One of the pair from each parent Example: each shoe is like a homologous chromosome in a pair of shoes Chromosomes and Chromosome Number

5. Sex Cells In order to perform sexual reproduction sex cells are used Sex cells have 23 chromosomes-half the usual number Sex cells have only one “shoe” of the pair

6. Haploid and Diploid cells –Haploid (n) cells have one set of chromosomes 23 chromosomes in humans Sex cells –Diploid (2n) cells have two sets Contain homologous pairs 46 chromosomes Body cells Chromosomes and Chromosome Number

7. Human Life Cycle Haploid and Diploid stages of the human life cycle.

8. Formation of Haploid Cells Meiosis reduces the number of chromosomes in a cell Cells end with half the number of chromosomes than the original cell. Creates leads to four haploid cells (gametes-sex cells) During meiosis chromosomes are copied once and then the nucleus divides twice during the two stages of meiosis

9. Meiosis I Meiosis II Meiosis I includes Prophase I Metaphase I Anaphase I Telophase I Produces two haploid cells Meiosis II includes prophase II metaphase II anaphase II telophase II Four new haploid cells result.

10. Meiosis I: reductive division. –Chromosome number from diploid to haploid Meiosis II: produces gamete cells –individual chromosomes

11. Meiosis I Prophase I: homologous pairs come together to form tetrads Tetrads Two homologous pairs that come together (4 chromatids) Nucleus disapears Centrioles move toward poles and spindle fibers begin to form

12. Meiosis I Metaphase I: Tetrads line up in middle Spindle fibers attach to the tetrads

13. Meiosis I Anaphase I: –Tetrads separate, centromeres odo not separate. –homologous chromosomes move toward the poles –Spindle fibers shorted

14. Meiosis I Telophase I: two haploid daughter cells doubled stranded homologous chromosomes Nucleus reforms

15. Meiosis II Prophase II: begins shortly after Telophase I. Nucleus disapears New spindle fibers forms around the homologous chromosomes. Centrioles move to poles

16. Meiosis II Metaphase II: –double stranded homologous chromosomes line up in middle –Spindle fibers attach to centromeres –Just like Mitosis!

17. Meiosis II Anaphase II: –centromeres separate, –individual chromatids move toward the poles

18. Meiosis II Telophase II: –nuclear membrane reforms –chromosomes unwind and become chromatin –four haploid daughter cells form

19. Mitosis and Meiosis

20. Summary

21. Meiosis Variability

22. Development of Gametes Spermatogenesis is the process by which sperm cells are produced. Oogenesis is the process that produces mature egg cells.