1. Meiosis

3. Homologous Chromosomes Homologous chromosomes: pairs of chromosomes with genes for the same traits, but they can have different information about those traits

4. ½ the chromosomes in a cell come from Mom, ½ the chromosomes in a cell come from Dad

5. Humans Humans have 46 chromosomes or 23 pairs of homologous chromosomes. Somatic (body) cells contain 46 chromosomes. 46 is the diploid (2n)number for humans. -Diploid means that a cell has both homologues for each chromosome Somatic cells reproduce by mitosis

6. The Homologues

7. Reproductive Cells Gametes(eggs and sperm) are called haploid because they contain one set of chromosomes. Eggs also called Ovum and sperm contain 23 chromosomes. Eggs and sperm are produced by meiosis- a process that reduces chromosomes by half

8. What is Meiosis? A type of cell division where ONE diploid cell (46 chromosomes) become FOUR haploid cells(23 chromosomes each). The cells produced by meiosis are gametes (sex cells)

9. One diploid cell gives rise to 4 haploid cells 46 23

10. Who does it? Plants Fungi Animals (including you) Males start meiosis at puberty. Females start meiosis in utero.

11. Where does it occur? In your gonads Females- the ovary Males-the testicles

12. Why does it occur? Genetic Variation Mixes genes from Mom and Dad to create a unique baby Reduce the chromosome number by half Ensures that each cell produced has one copy from each homologous pair of chromosomes 23 in sperm + 23 in egg unite (fertilization) leads to a 46 zygote(baby)

13. Meiosis creates the cells needed for sexual reproduction Two haploid gametes join to form one diploid cell. - the new diploid cell (fertilized egg) is called a zygote.

14. Quiz How many chromosomes does a human have? What are somatic cells? How do somatic cells reproduce? (process) How do sex cells reproduce? (process) A fertilized egg is called a ___________. What is the difference between haploid and diploid cells? Where in your body does meiosis occur?

15. How does it occur? In two stages called Meiosis I and Meiosis II. Each stage contains 4 distinct phases prophase metaphase anaphase teleophase telophase is followed by the division of cytoplasm known as cytokinesis.

16. Prophase 1 Homologous chromosomes join to form a tetrad -chromosomes in the tetrad cross over and exchange genes

17. Crossing over produces new genetic combinations - It is another way to increase genetic diversity

18. Independent Assortment During Metaphase 1, the tetrads ( groups of 4 homologous chromosomes ) line up down the center of the cell - they assort independently -Chromosomes from each parent line up independently of each other

19. Independent Assortment

20.  Independent assortment increases genetic diversity - There are 23 pairs of homologous chromosomes in humans - independent assortment ensures that there are 2 23 possible combinations 2 23 = 8,388,608 combinations - When two gametes join to form the zygote in fertilization the possible number of combinations is 2 23 X 2 23 = 64 trillion

21. Ovum Formation One egg is formed One daughter cell keeps ALL of the cytoplasm Other 3 daughter cells only have genetic material – Polar Bodies (Barr Bodies)

22. Sperm Formation Four sperm are formed. Cytoplasm and Nuclear Material Divides evenly. Flagella are added last to the cells.

24. Extra practice videos Meiosis stages video Amoeba sisters mitosis vs. meiosis review Mitosis Review Meiosis Song 1 Meiosis crash course