1. Meiosis!! Chapter 10

2. Meiosis  Purpose: to make sex cells  Gamete: sex cell  Male gamete= sperm  Female gamete= egg (ovum)

3. Let’s define the following words…  Meiosis:  Sexual reproduction- production of gametes  Gamete:  Sex Cells (egg and sperm)  Derived from germ cells  Somatic Cells:  Body Cells

4.  Haploid:  Half the chromosome number (n)  Cells with 1 of each pair of chromosomes (23)  Ex: Gametes  Diploid:  2 of each type of chromosome (2n)  Cells with twice the haploid number (46)  Ex: Somatic cells  Fertilization:  Sperm enters egg  Zygote:  Fertilized egg (diploid)

5. Chromosomes and Chromosome Number  Homologous chromosomes —set of chromosomes with same genes in same locations:  Get one from each parent  Somatic cells: 46 chromosomes  Gametes: 23 chromosomes

6. Sister chromatids One duplicated chromosome Centromere Homologous pair of chromosomes

7. Homologous Chromosomes  Same centromere position  Same length  Carry genes that control the same inherited traits

8. General Meiosis  The sexual life cycle in animals involves meiosis  Meiosis produces gametes (haploid)  When gametes combine in fertilization, the number of chromosomes is restored (diploid)

9. DNA Replication PrepareGrowth Division Mitosis Meiosis 2N NNNN

10. Karyotype

12. Meiosis  Like mitosis (PMAT), but 2 divisions:  Meiosis I (separation of homologous chromosomes)  Meiosis II (separation of sister chromatids)  Produces 4 daughter cells (NOT genetically identical!!!!!!)

13. Interphase  Same as Mitosis (G1, S, G2)  DNA- Chromatin  Centrioles- located near the nucleus  Nucleolus is present

14. Prophase I  Pairing of homologous chromosomes occurs forming a tetrad (Synapsis)  The nuclear envelope breaks down/nucleolus gone  Spindles form  Crossing over takes place

15. Crossing over  Homologous chromosomes exchange genetic material  Recombination of genes between chromosomes  How is crossing over related to genetic variation?

16. Metaphase I  Chromosome centromeres attach to spindle fibers  Homologous chromosomes line up at the equator

17. Anaphase I  Homologous chromosomes separate and move to opposite poles

18. Telophase I  The spindles break down  Chromosomes uncoil, 2 new nuclei form  The cell divides

19. Do Now!!  What gets separated in meiosis I? In meiosis II?  What is a tetrad?  What is the point of crossing over?

20. Prophase II  A second set of phases begins  Chromosomes condense again  Spindles form in each new cell

21. Metaphase II  Chromosomes line up at metaphase plate of each cell

22. Anaphase II  The sister chromatids are pulled apart at the centromere by spindle fibers  Move toward the opposite poles of the cell

23. Telophase II  The chromosomes reach the poles and the nuclear membrane and nuclei reform  Spindles break down

24. Cytokinesis o Cytokinesis results in four haploid cells (gametes) o Each with n number of chromosomes. *So… if the original diploid cell has 10 chromosomes, how many will each gamete have? *Why are the gametes NOT genetically identical?

26. Do Now!!  Match the description to the phase of meiosis. 1. Sister chromatids are pulled apart. _____ A. Prophase I 2. Homologous chromosomes line up in the middle of the cell._____ B. Metaphase I 3. 2 daughter cells are formed ____ C. Telophase I 4. Nuclear membrane disappears__ D. Anaphase II 5. Nuclear membrane reforms around 4 cells ____ E. Anaphase I 6. Homologous chromosomes are pulled apart ____ F. Telophase II

27. Crash course biology!!  https://www.youtube.com/watch?v=qCLmR9- YY7o

28. Spermatogenesis vs oogenesis

29. Genetic Variability  Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.  Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

30. Label the phases of meiosis