2. Meiosis Creating Gamete Cells

3. MEIOSIS: a process by which the number of homologous chromosomes per cell is reduced by half the number and is referred to as haploid cells (n).

4. Meiosis only happens in Gametes ( sex cells – egg or sperm) 46 chromosomes 23 pairs Human female karyotype

5. Human male karyotype 46 chromosomes 23 pairs

6. What are homologous chromosomes? a similar pair of chromosomes, one from the father & one from the mother

7. What is a Diploid Cell? A cell that contains 2 complete sets of homologous chromosomes is said to be diploid or 2n Somatic (body cells) are diploid cells. Blood cells Brain cells Nerve cells Liver cells

8. What is a Haploid Cell? A cell that contains 1 complete set of chromosomes. These are called gametes or sex cells (egg or sperm)

9. Meiosis: production of gametes Alternating stages –chromosome number must be reduced diploid  haploid 2n  n –humans: 46  23 meiosis reduces chromosome number makes gametes –fertilization restores chromosome number haploid  diploid n  2n haploid diploid

10. Meiosis I and Meiosis II resulting in 4 haploid daughter cells with “n” number of chromosomes There are 2 distinct divisions of meiosis: Interphase I Prophase I Metaphase I Anaphase I Telophase I Metaphase II Telephase II and Cytokinesis

11. Each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad. There are 4 chromatids in a tetrad. Meiosis I - Prophase I

12. Overview of meiosis I.P.M.A.T.P.M.A.T interphase 1prophase 1metaphase 1anaphase 1 telophase 1 prophase 2 metaphase 2anaphase 2telophase 2 2n = 4 n = 2

13. As homologous chromosomes pair up, they exchange genetic information in a process called crossing over producing new combinations of alleles – accounting for variation among species.

14. Sexual reproduction creates variability Sexual reproduction allows us to maintain both genetic similarity & differences. Baldwin brothers Jonas Brothers Martin & Charlie Sheen, Emilio Estevez

15. Gamete Formation in Meiosis 2n n n nn Sperm - male Egg- female Polar Bodies 2n n

16. Human Sperm + Human Egg Human Zygote 23 23 46 N N 2N Fertilization MitosisMeiosis CellsSomatic (body) Gametes (sex) ExamplesSkin, Blood Sperm, Egg Chromosomes 2n n Found ?All over body Testes, Ovaries CytokinesisOnceTwice

17. 2n n n nn MITOSISMEIOSIS