1. M EIOSIS F ORMATION OF G AMETES 1 https://www.youtube.com/watch?v=A2Xcm0t-kEM

2. HOMEWORK- D UE F RIDAY Take notes over chapter 10 in your STARR text. At least 3 bullet points per section One drawing per section There are 6 sections in this chapter so you should end up with 18 facts and 6 pictures. 2

3. W HY D O WE N EED M EIOSIS ?  It is the fundamental basis of sexual reproduction  Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote  Promotes genetic diversity (aka a better gene pool) 3

4. F ACTS A BOUT M EIOSIS  Daughter cells contain half the number of chromosomes as the original cell (haploid/1n)  Germ Cells- p roduce gametes  Makes sperm in the testes in males  spermatogenesis  Makes eggs in the ovaries in females  Oogenesis 4

5. M EIOSIS : T WO P ART C ELL D IVISION 5 Homologs separate Sister chromatids separate Haploid Meiosis I Meiosis II Diploid Haploid

6. F ERTILIZATION : P UTTING IT ALL TOGETHER 6 1n =3 2n = 6

7. R EPLICATION OF C HROMOSOMES  Replication is the process of duplicating a chromosome  Occurs prior to division  Replicated copies are called sister chromatids  Held together at centromere 7 Occurs in Interphase

8. A R EPLICATED C HROMOSOME 8 Homologs AKA Homologous pair Same genes, different alleles (versions of genes) Sister Chromatids Same genes, Same alleles Gene X Homologs separate in meiosis I and therefore different alleles separate. Gene: specific region of DNA that codes for a particular protein. Allele: any alternative form of a gene

9. T HE ORDER OF M EIOSIS Interphase Meiosis I PMAT C Meiosis II PMAT C Number of chromosomes In interphase the chromosome number duplicates 46x2 = 92 Meiosis I the chromosome number divides 92/2 = 46 Meiosis II the chromosome number divides again 46/2=23 9

10. M EIOSIS I: G ENETIC R ECOMBINATION 10 Nucleus Spindle fibers Nuclear envelope Early Prophase I (Chromosome number doubled from interphase) Late Prophase I Metaphase I Anaphase I Telophase I (haploid-only one chromosome type per cell)

11. P ROPHASE I 11 Early prophase Chromosomes condense. Spindle forms. Nuclear envelope fragments. Late prophase Homologs pair forming tetrad. Crossing over occurs

12. T ETRADS F ORM IN P ROPHASE I 12 Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Synapsis = putting the tetrads together

13. C ROSSING -O VER  Sister chromatids in a tetrad cross over each other  Pieces of chromosomes or genes are exchanged  Produces genetic recombination in the offspring  These are called homologous chromosomes 13

14. H OMOLOGOUS C HROMOSOMES D URING C ROSSING -O VER 14

15. C ROSSING -O VER 15

16. M ETAPHASE I 16 Homologous pairs (homologs) of chromosomes align along the equator of the cell

17. A NAPHASE I 17 Homologous pairs (homologs) separate and move to opposite poles. Sister chromatids remain attached at their centromeres.

18. T ELOPHASE I AND C YTOKINESIS 18 Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. Each cell is now haploid

19. M EIOSIS II: R EDUCING C HROMOSOME N UMBER 19 Prophase II Metaphase II Anaphase II Telophase II 4 haploid cells

20. P ROPHASE II 20 Nuclear envelope fragments. Spindle forms. DNA is NOT replicated.

21. M ETAPHASE II 21 Chromosomes align along equator of cell.

22. A NAPHASE II 22 Sister chromatids separate and move to opposite poles. Equator Pole

23. T ELOPHASE II AND C YTOKINESIS 23 Nuclear envelope assembles. Chromosomes uncoil. Spindle disappears. Cytokinesis divides cell into two.

24. R ESULTS OF M EIOSIS 24 Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome

25. Short intro https://www.youtube.com/watch?v=D1_-mQS_FZ0 Good detailed version of meiosis https://www.youtube.com/watch?v=rqPMp0U0HOA 25

26. 26 G AMETOGENESIS

27. S PERMATOGENESIS  Occurs in the testes  Two divisions produce 4 spermatids  Spermatids mature into sperm  Men produce about 250,000,000 sperm per day 27

28. S PERMATOGENESIS 28

29. O OGENESIS  Occurs in the ovaries  Two divisions produce 3 polar bodies that are recycled and 1 large egg  Polar bodies aren’t viable because of unequal division of cytoplasm  Immature egg called oocyte  Starting at puberty, one oocyte matures into an ovum (egg) every 28 days 29

30. O OGENESIS 30 Primary oocyte (diploid) Meiosis I Secondary oocyte (haploid) Meiosis II (if fertilization occurs) First polar body may divide (haploid) Polar bodies recycle Ovum (egg) (haploid) polar body a A X X a X A X a X a X Mature egg A X A X

31. C OMPARING M ITOSIS AND M EIOSIS 31

32. C OMPARISON OF D IVISIONS 32 MitosisMeiosis Number of divisions 1 2 Number of daughter cells 24 Genetically identical? YesNo Chromosome #Same as parentHalf of parent WhereSomatic cellsGerm cells WhenThroughout lifeAt sexual maturity RoleGrowth and repairSexual reproduction

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