Chromosomes: the cellular basis of the instructions Mitosis - Meiosis

1. Chromosomes: the cellular basis of the instructionsMitosis - Meiosis

2. Diploid organism: two sets of chromosomes ( one from each parent) • 2n • Haploid organism: one set of chromosomes • n

3. Germ cells: the cells that provide the continuity of life from generation to the next

4. Somatic cells: all the others

5. meiosis Haploid sperm Haploid egg Fertilization mitosis n n 2n

6. Mitosis

7. Metaphase Anaphase Prophase Telophase Interphase The cell cycle

9. Mitosis 2N Prophase Metaphase Anaphase Telophase 2N 2N 2C 4C 4C 2C 2C

10. Mitosis: Sister chromatids separate at anaphase

11. Diploid cells 2C 4C 4C Homologous chromatids 2C 2C Diploid cells

12. Meiosis

13. 2N 2C Prophase I 2N 4C 2N 4C 2N 4C 1N 2C 1N 2C 1N 1C

14. 1. Leptotene Prophase I 5.Diakinesis 4.Diplotene 2.Zygotene 3.Pachytene

15. 5.Diakinesis 4.Diplotene Prophase I

16. Crossing over Pairing of homologous chromosomes Chiasma formation Chromosomes Breakage and joining Recombinant chromosomes

17. Prophase I Metaphase I Anaphase I Telophase I Prophase II

18. Meiosis anaphase I :Homologous chromosomes separate Reduction from diploid to haploid

19. Meiosis 1st division: reduction from diploid to haploid number of chromosomestwo haploid cells

20. Prophase II Anaphase II Metaphase II Telophase II Meiosis 2nd division: like mitosis with haploid set

21. 4 Haploid cells Gametes

22. Meiosis begins by replicating the chromosomes This step is identical to mitosis

23. The homologous chromosomes then pairs Centromeres Do not split At meiosis I

24. 2n = 2C 2n = 4C Centromeres Do not split At meiosis I 2n = 4C Meiosis I is reductional n =2C

25. Centromeres Do split At meiosis II

26. Meiosis 1st division: reduction from diploid to haploid number of chromosomestwo haploid cells

27. Diploid cells Crossing over Homologous chromosomes Diploid to haploid Homologous chromatids Haploid cells

28. MITOSIS Somatic cells 2n 1 cell division: 2 daughter cells 2n 2n MEIOSIS Cells in sexual cycle 2 cell divisions: 4 product of meiosis n n 2n n n n=chromosome number

29. Mitosis Conservative process: Daughter cells genotypes identical to parental genotypes Meiosis Promotes variation among the product of meiosis (crossing over)

30. 30 mitotic divisions 15 years Puberty 4 mitotic divisions 2 meiotic divisions spermatids spermatozoa I II

31. X Bearing sperm egg ZYGOTE 2n 2n 2n Mitoses Growth and differentiation of organs and tissues 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n Somatic cells Female germ line 2n 2n 2n Proliferation of gonial cells 2n 2n oogonia 2n 2n

32. Primary oocytes 2n Meiosis I Secondary oocytes Polar body Meiosis II fertilization n Egg + 3 polar bodies

33. Female meiosis • Birth: diplotene of prophase I • At puberty every month: maturation = progress to metaphase II, release from the ovary • Penetration of the sperm: continue to anaphase II

34. Final result Mitosis : two genetically identical diploid cells from one diploid parent cell Meiosis : Four genetically different haploid cells from one diploid parent cell