Cell Division Mitosis and Meiosis

1. Cell DivisionMitosis and Meiosis

2. Types of Cell Division • Mitosis occurs in all body cells (somatic cells) in animals, plants, and humans • production of 2 identical daughter cells that are diploid • growth or replacement of body cells. • asexual reproduction. (offspring and parents are identical)

3. Types of Cell Division 2) Meiosis  occurs only is sex cells (sperm and egg) • production of the 4non-identical gametes (sex cells) that are haploid • Sperm and eggs have half the genetic information • sexual reproduction

5. The Cell Cycle • 10% time dividing (mitotic phase/meiotic phase) • 90% time interphase (G1, S, G2 phases)

6. Interphase 1) G1 (gap phase) -manufactures proteins and amino acids needed for both cell processes and cell division, carries out metabolic duties • Cell grows 2) S phase (synthesis phase) – DNA replicates. -longest stage of the cell cycle

7. 3) G2 (gap phase) • increases the rate of protein synthesis and prepares to divide. • grows larger

8. Division • Mitosis or Meiosis • cell can divide only about 50 times on average. • To ensure that the cells in a tissue are healthy, cells will undergo a form of cell suicide called apoptosis. • Cell Death

9. Terms • Chromatin – complex long threads made of DNA and protein that makes up chromosomes • Uncondensed chromosome – long, thin strands not visible with light microscope • Condensed chromosome – short and visible

11. Chromosome vs. Chromatid • Chromosomes replicate before division to form 2 matched sister chromatids

12. Ploidy • Humans have 46 chromosomes (diploid or 2N) • Sex gametes have 23 chromosomes (haploid or N • Some organisms have polyploidy • Ex) corn – 4n (tetraploidy)

13. –same size and shape and carry the genes for the same traits, but have different details Humans have 23 homologous chromosomes for a total of 46 Homologous chromosomes

14. Gene • basic unit of heredity • sequence of nucleotide bases in DNA. • codes for a specific proteins

15. Autosomes– chromosomes that do not influence gender (humans have 22 pairs of these) • Sex Chromosomes – X and Y chromosomes that determine gender in humans (humans have 1 pair of these, the 23rd chromosome pair)

16. Mitosis

17. Prophase(longest phase) • Early: chromatin condenses to form chromosomes, centrioles move to poles and attach to spindle fibres • Late: spindle fibres attach to centromere, nuclear membrane dissolves

18. Metaphase • chromosomes line up on the equatorial plate (center of the nucleus)

19. Anaphase • Spindle fibres contract from the centrioles and sister chromatids begin to separate apart, immediately chromosomes being to unravel

20. Telophase • nucleolus re-appears, nuclear membrane reforms, the chromosomes unravel to form a loose mass of chromatin • cells undergo cytokinesis (divide cytoplasm)

21. a cell plate forms between the new daughter cells the cell membrane pinches in between the two daughter cells Plant vs Animal Cells

22. Mitosis Overall • http://www.loci.wisc.edu/outreach/bioclips/CDBio.html

23. Some Methods of Asexual Reproduction 1.  Binary fission - equal division of both the organism cytoplasm and nucleus to form two identical organisms ex: Protist, amoeba 

24. 2) Budding - one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally ex: Fungi-  yeast

25. Meiosis – Sexual Cell Division Occurs in sexual reproduction The end result is 4 gamates that are genetically different Spermatagonium4 sperms Oogonium 4 eggs

26. Meiosis I – Reduction Division Prophase I – homologous chromosomes undergo synapsis (pair up) and crossing over occurs. -also, as in mitosis prophase: Chromos condense Nuclear membrane disappears Centrioles move to opposite poles -tetrad

27. Metaphase I – homologous pairs line up along the equatorial plate, spindles insert into the centromeres.

28. Anaphase I – homologous chromosomes separate and are pulled to opposite poles = segregation

29. Chromosomes undergo independent assortment in during Anaphase I -increases genetic diversity

30. Telophase I – daughter cells separate, each has one chromosome from each homologous pair. -reduction has occurred so that the new cells will be haploid (n) • -cytokinesis occurs

31. Meiosis II – like mitosis but no initial replication of DNA-very brief, not as long as meiosis I • Prophase II –spindles form

32. Metaphase II –chromosomes align at the equatorial plate

33. Anaphase II – the daughter chromatids separate and move towards separate poles

34. Telophase II – spindle fibres disappear, nuclei reform and cytokinesis takes place. (All 4 daughter cells are haploid.)

35. How many genetic combinations of gamates? • The number of possible chromosome combination in a gamate is 2^n • Where ‘n’ is the haploid number • Ex. Humans n=23, thus 2^23 =8, 388, 608 different combinations!! • Now THAT’S diversity!!

36. NOVA Online | 18 Ways to Make a Baby | How Cells Divide: Mitosis vs. Meiosis (Flash)

37. Human Life Cycle

38. Fern Life Cycle

39. Oogenesis

40. Spermatogenesis

41. Oogenesis (female) meiosis II completes only if egg is fertilized Secondary oocyte receives most of the cytoplasm and becomes the egg polar bodies have less cytoplasm and degenerate one egg cell is produced Spermatogenesis (male) meiosis I and II are both completed before fertilization each sperm cell produced receives an equal share of cytoplasm flagellum forms from one of the centrioles four spermatids are produced Oogenesis vs Spermatogenesis

42. Human Karyotype Chart

43. Gender • Female is XX • Male is XY XX XY

44. Chromosomal abnormalities can be detected by doing a karyotype chart. • Fetal cells are collected through amniocentesis or chorionic villi sampling

45. Successful cell division relies on 2 things: 1. accurate replication of the chromosomes 2. exact separation / distribution of the chromosomes

46. Trisomy –three chromosomes replace a normal pair (47 chromosomes in humans)

47. Abnormal Meiosis • Non-disjunction – occurs during meiosis when two homologous chromosomes move to the same pole. Chromosomes do not separate properly Normal Division Non-disjunction

48. Some Common Genetic Disorders Down’s syndrome – trisomy 21 • Extra 21 chromosome • more common in children born to women over 40 • characterized by short stature, folds to the eyelids, stubby fingers, wide gap between 1st and 3rd toes, large fissured tongue, round head, palm creases, mild to severe mental retardation.

50. Edward’s syndrome – trisomy 18 • results in severe overall defects with a life expectance of only 10 weeks Patau’s syndrome – trisomy 13 • results in non-functioning eyes, severe deficits and limited life expectancy.