1. 6.2 Process of Meiosis KEY CONCEPT Meiosis creates sex cells that are haploid

2. The Process of Meiosis One parent cell produces 4 gametes/sex cells Sex cells have half the chromosome number (haploid) as the parent cell (diploid) Daughter cells are genetically different than parent cell

3. 6.2 Process of Meiosis Meiosis is also known as Reduction Division because as the cell divides, its chromosome number is reduced

4. 6.2 Process of Meiosis Why must the genetic material be reduced? n (sperm) + n (egg) = 2n (zygote) from momfrom dadchild meiosis reduces genetic content Too many! Just right!

5. 6.2 Process of Meiosis Meiosis occurs in 2 Stages: Meiosis I and Meiosis II

6. In Meiosis I homologous chromosome pairs separate

7. In Meiosis II sister chromatids separate

8. 6.2 Process of Meiosis : Meiosis I (ANAPHASE I ) – Homologous Chromosome Pairs separate. Haploid n Diploid 2n

9. 6.2 Process of Meiosis : Meiosis I (ANAPHASE I ) – Homologous Chromosome Pairs separate. Haploid n Diploid 2n

10. 6.2 Process of Meiosis : Meiosis I Meiosis II Homologous chromosomes separate. Haploid n Diploid 2n Haploid n Sister chromatids separate

11. Sister Chromatids Sister chromatids – * Made in Interphase “S” * Genetically identical Sister Chromatids Homologous Chromosomes – * One inherited from each parent * Similar gene segments but NOT identical WHAT’S THE DIFF????

12. Interphase I Cell carries out job Chromosomes stringy chromatin Chromosomes duplicated in “S” apart.

13. Prophase I (Early) Chromosomes condense (coil) Nuclear membrane breaks apart Spindle fibers form.

14. Prophase I Late Homologous chromosomes synapse and exchange DNA segments – crossing over Increases genetic diversity cause each chromosome now has genes from both parents mixed together

15. C rossing Over – Increases genetic diversity C rossing Over – Increases genetic diversity This increases genetic diversity important for survival and evolution

16. Metaphase I Homologous chromosomes line up side by side on the equator and attach to the same spindle fiber

17. Anaphase I Homologous chromosomes separate and move to opposite poles. Each pole receives only 1 copy of each chromosome

18. Telophase I and Cytokinesis Nuclear envelopes reforms Spindle fibers disappear Cytokinesis divides the cytoplasm into two cells

19. End of Meiosis I Results of Meiosis I 2 Haploid Cells No doubling of chromosomes occurs before Meiosis II

20. Meiosis II Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four Non-identical haploid daughter cells

21. Prophase II Nuclear envelope breaks apart Spindle forms.

22. Metaphase II Chromosomes line up on cell equator

23. Anaphase II Sister chromatids separate and move to opposite poles.

24. Telophase II and Cytokinesis Nuclear envelope forms Spindle fibers disappear Chromosomes unravel. Cytokinesis divides the cell’s cytoplasm into two cells

25. End of Meiosis II 4 Cells with Haploid # Each cell is genetically unique

26. Gametogenesis – Process of Haploid cells developing into mature gametes In males meiosis occurs in the testicles and forms sperm In females meiosis occurs in the ovaries and forms eggs

27. 6.2 Process of Meiosis SPERMATOGENESI S Sperm get flagella and become swimmers. Sperm mainly contribute DNA to an embryo.

28. 6.2 Process of Meiosis OOGENESIS Eggs contribute DNA, cytoplasm, and organelles to an embryo. Cytoplasm divides unevenly - the egg gets most of the contents; the other cells form 3 polar bodies which can’t be fertilized.

29. “Putting It All Together” - Fertilization

30. What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction. Meiosis Video Link

31.  Meiosis Video Link #1 Meiosis Video Link #1 Meiosis Video Link #1  Meiosis Video Link #2 Meiosis Video Link #2 Meiosis Video Link #2  Meiosis Video Link#3 Meiosis Video Link#3 Meiosis Video Link#3

32. Problems in Meiosis  Nondisjunction – Failure of chromosomes to separate during Anaphase I or II  Results in too many or too few chromosomes in offspring chromosomes in offspring

34. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Meiotic Non-disjunction (Trisomy 21: 75% meiosis 1) Trisomy Monosomy (lethal)

35. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Nondisjunction of Autosomes Trisomy 21 – Down’s Syndrome Trisomy 13 – Patau’s Syndrome

36. Down’s Syndrome – Trisomy 21

37. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Patau Syndrome - Trisomy 13

38. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Nondisjunction - Sex Chromosomes Turner’s Syndrome – X Klinefelter’s Syndrome - XXY

39. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk

40. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk

41. 6.2 Process of Meiosis Meiosis differs from mitosis in significant ways. –Meiosis has two cell divisions while mitosis has one.

42. 6.2 Process of Meiosis MitosisMeiosis Number of divisions12 Number of daughter cells made through process 24 Are the new cells Genetically identical? YesNo # of Chromosomes compared to parent cell Same as parentHalf of parent What cell go thru this division process Somatic cellsSex cells When do cells go thru this division process Throughout lifeAt sexual maturity RoleGrowth and repairSexual reproduction

43. 6.2 Process of Meiosis MITOSISMEIOSIS Occurs in somatic (body) cellsOccurs only in gonads (sex organs: ovary/testes) Produces cells for repair, maintenance, growth, asexual reproduction Only produces gametes (sex cells: egg/sperm) Results in identical diploid (2n) daughter cells Reduction division results in haploid (n) cells

44. 6.2 Process of Meiosis Mitosis or Meiosis? 2 diploid 4 haploid Crossing over between nonsister chromatids Reduction division Increases genetic variability vs. clones Meiosis 1 Homologous chrom separate Meiosis 2 Sister chromatids separate

45. 6.2 Process of Meiosis Mitosis or Meiosis? 2 diploid 4 haploid Crossing over between nonsister chromatids Reduction division Increases genetic variability vs. clones Meiosis 1 Homologous chrom separate Meiosis 2 Sister chromatids separate

46. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Parental origin of meiotic error leading to aneuploidy