1. Reduction-Division Genetic Recombination https://www.youtube.com/w atch?v=toWK0fIyFlY 1

2. cell division GAMETES, HALF CHROMOSOMES,  The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced.  DIPLOID (2n)  HAPLOID (n)  MeiosisSEXUAL reproduction.  Meiosis is SEXUAL reproduction.  TWO divisionsMEIOSIS I MEIOSIS II  TWO divisions (MEIOSIS I and MEIOSIS II). 2

3. GAMETES(sperm or egg)  Sex cells divide to produce GAMETES (sperm or egg). HALF  Gametes have HALF the # of chromosomes. GONADS (testes or ovaries).  Occurs only in GONADS (testes or ovaries).  Male: sperm  Female: egg 3

4. mitosis  Similar to mitosis interphase.  CHROMOSOMES (DNA) S phase  CHROMOSOMES (DNA) replicate in the S phase chromosometwo identical SISTER CHROMATIDS CENTROMERES  Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES.  CENTRIOLE  CENTRIOLE pairs also replicate. 4

5. visible  Nucleus and nucleolus visible. Nucleus nucleolus cell membrane chromatin 5

6.  Cell division chromosome number one- half.  Cell division that reduces the chromosome number by one- half.  Four phases  Four phases: a.Prophase I b.Metaphase I c.Anaphase I d.Telophase I 6 Prophase I

7.  Longest and most complex phase (90%).  Chromosomes  Chromosomes condense.  SynapsisHomologous chromosomes tetrad  Synapsis occurs - Homologous chromosomes come together to form a tetrad.  Tetrad two chromosomes four chromatids  Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). 7

8. 8 Homologs contain DNA that codes for the same genes, but different versions of those genes

9. Homologous chromosomes sister chromatids Tetrad 9

10. chromosomesmaternal paternalsimilar in shape and size.  Pair of chromosomes (maternal and paternal) that are similar in shape and size. (tetrads) carry GENES controlling the SAME inherited traits  Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits. 10

11. PaternalMaternal eye color locus eye color locus hair color locus hair color locus 11

12.  Crossing over chromatids chiasmata  Crossing over may occur between non-sister chromatids at sites called chiasmata.  Crossing over chromatids chromatid  Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.  Chiasmata (chiasma) exchange genes crossing over  Chiasmata (chiasma) are where chromosomes touch each other and exchange genes (crossing over.) Genetic Recombination  Causes Genetic Recombination 12

13. nonsister chromatids chiasmata: site of crossing over variation Tetrad 13

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15. XX chromosome - female XY chromosome - male 15

16. Homologs separate 16 Meiosis I

17. Nucleus & Nucleolus Nucleus & Nucleolus disappear Spindle Spindle forms coilSynapsis Chromosomes coil & Synapsis (pairing) occurs Tetrads Crossing over Tetrads form & Crossing over Occurs centrioles spindle fiber aster fibers 17 TETRAD

18.  Shortest phase  Tetrads align on the equator.  Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION 18

19. Homologs line up at equator or metaphase plate OR 19

20.  Homologous chromosomes  Homologous chromosomes separate and move towards the poles.  Sister chromatids centromeres  Sister chromatids remain attached at their centromeres. 20

21. 21 Homologs separate Homologs separate

22. haploid chromosomes  Each pole now has haploid (1n) set of chromosomes.  Cytokinesis  Cytokinesis occurs and two haploid daughter cells are formed. 22

23. 23 cytokinesis

24. Sister Chromatids Separate 24 Meiosis II

25.  No Interphase II or very short  No DNA Replication  Remember: Meiosis II is similar to mitosis 25

26.  Same as Prophase in mitosis  Nucleus & nucleolus disappear  Chromosomes condense  Spindle forms 26

27.  Same as Metaphase in mitosis Chromosomes (not homologs) line up at equator 27

28. Anaphasemitosis  Same as Anaphase in mitosis  SISTER CHROMATIDS separate 28

29.  Same as Telophase in mitosis.  Nuclei and Nucleoli reform, spindle disappears  CYTOKINESIS occurs.  Remember: FOUR HAPLOID DAUGHTER cells are produced.  Called GAMETES (eggs and sperm) 29 1n Sperm cell fertilizes 1n egg to form 2n zygote

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