Copy-of-Meiosis cell division s hjj-2.pptx

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1. Meiosis 1 and ii: life cycles

2. body cells or autosomes=46 chromosomes sex cells= 23 chromosomes

3. meiosis a process of cell division in which diploid cells divide to produce genetically distinct haploid cells.

4. meiosis a process of cell division in which diploid cells divide to produce genetically distinct haploid cells.

5. meiosis a process of cell division in which diploid cells divide to produce genetically distinct haploid cells. Gametes created (egg and sperm) End Result: Four haploid cells

6. Stages of cell cycle: meiosis Interphase G1 (First gap) S (Synthesis stage) G2 (Second gap) Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

7. First meiotic division The first meiotic division results in reducing the number of chromosomes (reduction division). In most cases, the division is accompanied by cytokinesis.

8. Prophase i Has been subdivided into five substages: Leptonema Zygonema Pachynema Diplonema and Diakinesis

9. 1. Leptonema Replicated chromosomes have coiled and are already visible. Number of chromosomes present is the same as the number in the diploid cell.

10. 2. zygonema Homologue chromosomes begin to pair and twist around each other in a highly specific manner. The pairing is called synapsis. And because the pair consists of four chromatids it is referred to as bivalent tetrad.

11. 3. pachynema Chromosomes become much shorter and thicker. crossing – over , a form of physical exchange of chromosomal region between homologous chromosomes, takes place.

12. 4. diplonema After the crossing – over process, the pair of homologous chromosomes begin to separate from each other and the area of contact between two non – sister chromatids during crossing – over, called chiasma , become more evident.

13. 5. diakinesis In this stage, the homologous chromosomes separate further, and the chiasma terminalize. Making chiasmata clearly visible.

14. Prometaphase I nucleus and other organelles are no longer visible. centrioles have reached the opposite poles of the cell. Spindle fibers converge and attach to each bivalent tetrad from both poles, with one homologous chromosome facing each pole.

15. Metaphase i The synapsed tetrads are found aligned at the metaphase plate (equatorial plane of the cell) instead of only replicated chromosomes.

16. Anaphase i Chromosomes in each tetrad separate and migrate towards the opposite poles. The sister chromatids (dyads) remain attached at their respective centromere regions.

17. Telophase I The dyads have reached the opposite poles of the cell. The spindle fibers start to disappear. Nuclei and cytoplasmic contents of the daughter cells start to reform.

18. Cytokinesis of Meiosis I nuclei and cytoplasmic contents of the daughter cells are fully visible. The constriction continues forming the cleavage furrow , which pinches the cell in two. Two new daughter cells are formed, each with only one set of chromosomes (haploid) in a replicated form.

19. Given that the number of chromosomes in the parent cell is 6 (2n), how many chromosomes will each daughter cells have after telophase I? Prophase I Metaphase I Anaphase I End of Telophase I Number of Chromosomes 6 6 6

20. Given that the number of chromosomes in the parent cell is 6 (2n), how many chromosomes will each daughter cells have after telophase I? Prophase I Metaphase I Anaphase I End of Telophase I Number of Chromosomes 6 6 6 3

21. MEIOSIS II No interphase II ( no more DNA duplication ) Remember: Meiosis II is similar to mitosis Prophase II / Metaphase II Anaphase II

22. Prophase II chromatin materials start to condense, forming discrete chromosomes. nucleus and other organelles of the cell start to disintegrate.

23. Prometaphase II The centrioles have reached the opposite poles of the cell. Spindle fibers converge and connect to the kinetochore of chromosomes forcing them to move toward the center of the cell.

24. Metaphase II chromosomes convene on the metaphase plate.

25. Anaphase II Anaphase begins when the centromere of each chromosome come apart, separating the sister chromatids ( monads ).

26. Telophase II The monads have reached the opposite poles of the cell. The spindle fibers start to disappear. Nuclei and cytoplasmic contents of the daughter cells start to reform.

27. Cytokinesis of Meiosis II The constriction continues forming the cleavage furrow, which pinches the cell in two. Four new daughter cells are formed, each with the haploid number of chromosomes.

28. Given that the number of chromosomes in the parent cell is 6 (2n), how many chromosomes will each daughter cells have after telophase II? Prophase I Metaphase I Anaphase I End of Telophase I Number of Chromosomes 3 3 3

29. Given that the number of chromosomes in the parent cell is 6 (2n), how many chromosomes will each daughter cells have after telophase I? Prophase I Metaphase I Anaphase I End of Telophase I Number of Chromosomes 3 3 3 3

30. Mitosis vs Meiosis Mitosis Body (somatic cells) 2 daughter cells made (identical) Each w/ same # & kind of chrom. as parent cell 1 division process 1 cytokinesis No synapsis or crossing over Are diploid (2n) Meiosis Germ cells of gonads 4 gamete cells made (all different) Each w/ ½ chrom. # as parent cell 2 divisions 2 cytokineses events Synapsis & crossing over occurs in Prophase 1 Are haploid (n)

31. Oogenesis 2n = 46 human germ cell in ovary diploid (2n) n=23 Still doubled n=23 Still doubled meiosis I 23 23 23 Ovum n=23 Polar Bodies meiosis II

32. Spermatogenesis 2n = 46 human germ cell in testes diploid (2n) n=23 Still doubled chromosomes n=23 Still doubled chromosomes meiosis I n=23 n=23 n=23 n=23 sperm haploid (n) meiosis II

33. Changes in chromosome number

34. Changes in chromosomes number Change in Chromosome No. Chromosome Number Examples Trisomy 2n+1 Trisomy-13 (Patau’s Syndrome) Trisomy-18 (Edward’s Syndrome) Trisomy-21 (Down Syndrome) Monosomy 2n-1 Monosomy X (Turner’s Syndrome)

35. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Monosomy Turner’s syndrome Has only one X chromosomes in the 23rd pair The affected individual is female, short, with webbing of the neck, has a low hairline on the back of the neck, has a broad chest, exhibits slight mental deficiency, and the breasts, the external genital organ, and secondary characteristics do not develop

36. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Trisomy Down’s syndrome Has an extra copy of chromosome in the 21st pair The mouth is usually open, slanting eyes, upper eyelid appears bulging or swollen, usually a low nose bridge, low – set ears, short broad hands with abnormal palm prints, mentally retarded, with heart and respiratory ailments, and a reduced life expectancy. Edward’s syndrome Has an extra copy of chromosome in the 18th pair The jaws are small, clenched fingers, harelips, cleft palates, malformations of the heart, skull, face, and feet, severely mentally retarded, and die at three to four months of age.

37. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Trisomy Patau’s syndrome Has an extra copy of chromosome in the 13th pair There is deformation of hands and feet, as well as a face severely deformed by a cleft lip and cleft palate, and live from about a few days to a few months.

38. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Trisomy Klinefelter’s syndrome Has an extra copy of X chromosome and one Y chromosome in the 23rd pair The affected individual is male, has a general male appearance, the testes are usually small, sperm cells are usually not produced, most are mentally handicapped, the arms are longer than average, the breasts are slightly developed, the voice has a higher pitch than in normal males.

39. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Trisomy Metafemale or Triple X syndrome Has three to four X chromosomes in the 23rd pair The affected individual is female, does not have distinct clinical features but may have menstrual irregularities, secondary amenorrhea, and premature menopause, generally has subnormal mental abilities. Metamales or Double Y syndrome Has an extra copy of Y chromosome and one X chromosome in the 23rd pair The affected individual is male, tall, with low IQ, with severe facial acne during adolescence, severely mentally retarded.

40. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Deletion Cri – du – chat or cat – cry syndrome Deletion of a segment of a chromosome in the 5th pair The affected individual has a characteristic high – pitched cry during infancy similar to a kitten in distress, malformed head and face, severely mentally retarded, with low IQ, and malformed and improperly functioning brain, heart, eyes, kidneys, bones, and larynx.

41. Chromosomal aberrations Error in the structure or number of chromosomes Characteristic properties Deletion William’s syndrome Deletion of a segment of a chromosome in the 7th pair The affected individual has broad forehead, flat nasal bridge, lower eyelid appears bulging or swollen, full lips, wide mouth, very active, and with cognitive impairment and developmental delays.