Cell Division & Cell Cycle

1. Cell Division & Cell Cycle Comparing Mitosis and Meiosis

2. Cell Division • Cell Division-when a parent cell divides into two daughter cells. • All body cells are somaticcells and divide by mitosis • Sperm and egg, which are gametes (sex cells) divide by meiosis

3. Cell Division • Mitosis-the nucleus of the cell divides equally Parent Cell Two identical daughter cells

4. Eukaryotic Cell Cycle Period between cell division DNA is Copied Organelles form&Cells prepares to Divide Synthesis phase Cells Mature Gap 1 phase Gap 2 phase Daughter Cells Cell nucleus divides equally Cytoplasm Divides

5. Cell Cycle Remember: I P M A T C • I = Interphase (G1, S, G2) • P = Prophase • M= Metaphase • A= Anaphase • T= Telophase • C= Cytokinesis

6. Interphase: Part 1 of Cell Cycle • Interphase-cell prepares for cell division. • Genetic Material (DNA)-is in the form of chromatin-uncoiled chromosomes • Has 3 phases: G1, S, G2

7. Eukaryotic Chromosomes • Eukaryotecells store genetic info.in tightly coiled DNA segments orchromosomes • Human body cells =46 chromosomes Chromosomes can’t be seen when cells aren’t dividingand are called chromatin • Chromatin-uncoiled chromosomes

8. Chromosome Pictures • Duplicated chromosomes are called sisterchromatids & are held together by the centromere-found at the center of the chromosome Sister Chromatids

9. Mitosis: Part 2 Of Cell Cycle • Mitosis-is equal division of the nucleus of eukaryote cells Has four stages: • P rophase • Metaphase • Anaphase • Telophase

10. Prophase • Prophase-first and longest phase of mitosis • Nucleolus and nuclear envelope will disappear • Chromosomes are now visible and are attached to the spindle • The Spindle-(a fan-like structure that pulls the chromosomes apart) appears. • Centrioles-(two tiny structures in the cytoplasm that travel toward opposite sides of the nucleus) in animal cells help to form the spindle

11. Metaphase • Second, shortest phase of mitosis; lasts a few minutes • Chromosomes are now lined up at the equator or center of the cell Equator of Cell Pole of the Cell

12. Anaphase Spindle is pulling the sister chromatids apart Spindle sister chromatids Sister Chromatids being separated

13. Telophase • Sister chromatids are at opposite poles • Spindle breaks apart • Nuclear envelope forms around each set of sister chromatids • Nucleolus reappears • Chromosomes reappear as chromatin

14. Cytokinesis • Means division of the cytoplasm • Division of cell into two, identical halves called daughter cells • In plant cells, cell plateforms at the equator to divide cell • In animal cells, cleavage furrow forms to split cell

15. Identical Daughter Cells Mitosis-goes from diploid to diploid What is the 2n or diploid chromosomenumber in humans? 46 46 46 46 Chromosome number is maintained or is the same (Diploid), but cells smaller than parent cell

16. MeiosisFormation of Gametes(Eggs & Sperm)

17. Facts About Meiosis • Interphase occurs before meiosis;chromosome replicationoccurs • Twomeiotic divisions-Meiosis I and Meiosis II • Called Reduction Division-chromosome # is reduced by ½ (4623) • Original cell is diploid (2n)=46 • Four daughter cellsproduced at the end of meiosis are monoploid (n) or haploid (chromosomes reduced by½)

18. Facts About Meiosis • Daughter cellscontain half (23) the number of chromosomesas the original cell (46) • Meiosis producesgametes(eggs & sperm) • Occurs in the testes in males (Spermatogenesis) • Occurs in the ovaries in females (Oogenesis)

19. Why Do we Need Meiosis? • It is the fundamental basis of sexual reproduction • Two haploid (n) gametes are brought together through fertilization to form a diploid (2n) zygote

20. from mom from dad child too much! meiosis reduces genetic content Meiosis Forms Haploid Gametes • Meiosis must reduce the chromosome number by half • Fertilization then restores the 2n number The right number!

21. Prophase I • Late prophase • Chromosomes condense. • Spindle forms. • Nuclear envelope fragments. • Early prophase • Homologs pair. • Crossing over occurs.

22. Crossing-Over • Homologous chromosomes in a tetrad cross over each other • Pieces of chromosomes or genes are exchanged • Produces Genetic recombination in the offspring

23. Metaphase I Homologous pairs of chromosomes align along the equator of the cell

24. Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres.

25. Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.

26. Sister chromatids carry identical genetic information. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Meiosis II Only one homolog of each chromosome is present in the cell. Gene X

27. Meiosis II: Reducing Chromosome Number Prophase II Metaphase II Telophase II Anaphase II 4 Identical haploid cells

28. Prophase II Nuclear envelope fragments. Spindle forms.

29. Metaphase II Chromosomes align along equator of cell.

30. Anaphase II Equator Pole Sister chromatids separate and move to opposite poles.

31. Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two.

32. Results of Meiosis 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

33. Spermatogenesis • Occurs in the testes • Two divisions produce 4 spermatids • Spermatids mature into sperm • Men produce about 250,000,000 sperm per day

34. Spermatogenesis in the Testes Spermatid

35. Oogenesis • Occurs in the ovaries • Two divisions produce 3 polar bodies that die and 1 functional egg • Polar bodies die because of unequal division of cytoplasm • Immature egg is called an oocyte • Starting at puberty, one oocyte matures into an ovum (egg) every 28 days

36. Comparing Mitosis and Meiosis

37. Karyotype • A picture of the chromosomes from a human cell arranged in pairs by size • First 22 pairs are called autosomes • Last pair are the sex chromosomes • XX female or XY male

38. Nondisjunction • When chromosomes fail to separate during Anaphase I or Anaphase II of meiosis • Chromosome number can be more (47) or less (45), than the normal chromosome number (46) • Example: Down’s Syndrome-has extra chromosome on #21 also called Trisomy 21

39. Quiz 1. If a cat has 38 chromosomes in each of its body cells, how many chromosomes will be in each daughter cell after mitosis? F 11 G 19 H 38 J 76

40. Quiz 2. If a cat has 38 chromosomes in each of its cells, how many chromosomes will be in each gamete after meiosis? F 11 G 19 H 38 J 76

41. Quiz 3. Which of these symbols represents the normal karyotype of a human female? F XXY G XX H XO J XXX

42. Quiz 4. This human karyotype is unusual because chromosome set — A 5 has chromosomes of different shapes B 10 is missing genetic material C 14 has enlarged centromeres D 21 has extra genetic material Unusual Human Karyotype

43. Quiz 5. The diagram represents the chromosomes of a person with a genetic disorder caused by nondisjunction, in which the chromosomes fail to separate properly. Which chromosome set displays nondisjunction? F 2 G 8 H 21 J 23

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