Meiosis is the cell division process that produces gametes, or sex cells, in sexual reproduction. It involves two rounds of cell division to reduce the chromosome number from diploid to haploid. This ensures that fertilization results in a diploid cell with the proper chromosome number. Meiosis I separates homologous chromosome pairs, reducing the number from 2n to n. Meiosis II then separates sister chromatids, resulting in four haploid daughter cells each with one copy of each chromosome type.

1. Cell Division SOL: BIO 6 a-c

2. Meiosis: Important Vocabulary Diploid- contains 2 sets of chromosomes (2n = 46) Example: human somatic cells Haploid- contains 1 set of chromosomes (n = 23) Example: human gametes

3. Meiosis: Important Vocabulary Fertilization- fusion of two haploid gametes forms a diploid zygote Zygote- fertilized egg cell The first cell of a new individual What would happen if gametes were diploid?

4. Meiosis Meiosis occurs in sexual reproduction when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg).

5. Meiosis Goal: reduce genetic material by half Why? n (mom) + n (dad) = 2n (offspring) Just right! from mom from dad child meiosis reduces genetic content too much!

6. Meiosis: cell division in two parts Chromatids separate Sister chromatids separate Result: one copy of each chromosome in a gamete. (equational division) 2n n Diploid 2n Diploid Meiosis I (reduction division) Meiosis II Haploid

7. Meiosis I : the reduction division Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) Nucleus Spindle fibers Nuclear envelope

8. Prophase I Early prophase Chromatids pair. Crossing over occurs. Late prophase Chromosomes condense. Spindle forms. Nuclear envelope fragments.

9. Metaphase I Chromatid pairs align along the equator of the cell.

10. Anaphase I Chromosomes separate and move to opposite poles. Sister chromatids remain Attached at their centromeres.

11. Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.

12. Meiosis II Gene X Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Sister chromatids carry identical genetic information .

13. Meiosis II : the equational division Prophase II (diploid) Metaphase II Anaphase II Telophase II Four Non-identical haploid daughter cells

14. Prophase II Nuclear envelope fragments. Spindle forms.

15. Metaphase II Chromosomes align along equator of cell.

16. Anaphase II Sister chromatids separate and move to opposite poles.

17. Telophase II Nuclear envelope assembles. Chromosomes unravel. Spindle disappears. Cytokinesis divides cell into two.

18. Results of meiosis Four haploid cells One copy of each chromosome

19. “ Putting It All Together” - Fertilization

20. What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction.

21. Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Sex cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction

22. MITOSIS MEIOSIS Occurs in somatic (body) cells Occurs only in gonads (sex organs: ovary/testes) Produces cells for repair, maintenance, growth, asexual reproduction Only produces gametes (sex cells: egg/sperm) Results in identical diploid (2n) daughter cells Reduction division results in 4 haploid (n) cells