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CELL DIVISION

CELL DIVISION. By Fulden Donangil. Figure 1. Types of Cell Division:. 1-Mitosis 2-Meiosis. MITOSIS. Mitosis is a kind of cell divison which occurs in somatic cells and results in two daughter cells.

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CELL DIVISION

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  1. CELL DIVISION By Fulden Donangil Figure 1

  2. Types of Cell Division: • 1-Mitosis • 2-Meiosis

  3. MITOSIS • Mitosis is a kind of cell divison which occurs in somatic cells and results in two daughter cells. • These daughter cells are identical to each other and to the parent cell. • Daughter cells are diploid which means that they they have 2 sets of chromosomes. • One set of chromosomes is donated from the mother and the other set of chromosome donated from father.

  4. There are 5 stages of Mitosis • 1-Interphase • 2-Prophase • 3-Metaphase • 4-Anaphase • 5-Telophase Figure 2

  5. Interphase • There are 3 stages in interphase; • -G1: The cells grow and get bigger for the division. • -S : DNA is synthesized by the process of DNA Replication. • -G2 : Mitochondria and other organelles divide. Figure 3

  6. Prophase • Chromosomes become shorter and fatter. • They move to opposite poles of the cell and spindle fibres are formed. • Nucleolus disappears. • Nuclear membrane breaks down Figure 4

  7. Metaphase • Chromosomes line up at the equator individually. • Spindle fibers attachto chromosomes at the centromere. Figure 5

  8. Anaphase • Spindle fibres pull chromosomes apart. • Microtubules shortening. • Centromere of each chromosomes breaks down. • Daughter chromosomes travels to opposite poles. Figure 6

  9. Telophase • All chromosomes are at opposite poles. • Spindle fibres break down. • Nuclear envelope reformed. • Chromosomes become invisible. Figure 7

  10. Animation of Mitosis http://www.cellsalive.com/mitosis.htm

  11. MEIOSIS • Meiosis is a kind of cell division which occurs in gametes(sperms and eggs) and results in four daughter cells. • Daughter cells are genetically different from each other and from parent cells. • Daughter cells are haploid which means that they have one complete set of chromosomes. • During meiosis DNA replicates once but the nucleus divides twice. Therefore two division occur in meiosis.

  12. Importance of Meiosis • It halves the chromosome number. • It is important to have a diploid cell with correct number of chromosome(46 chromosome). • It increases variation.

  13. First Division of Meiosis • Prophase 1 • Metaphase 1 • Anaphase 1 • Telophase 1

  14. Prophase 1 • Most of the steps are same as in the mitosis except; • Homologous chromosomes pair up to from bivalent consisting of 4 chromatids. • Two chromosomes can overlap with each other which is known as CROSSING OVER.

  15. Metaphase 1 • Most of the steps are same as mitosis except; • Spindle fibres move bivalent chromosomes to line up at the equator instead of single chromosomes.

  16. Anaphase 1 • The centromeres do not divide • One chromosome from each homologous pair moves to each end of the cell. • As a result, the chromosome number in each cell is half of the original.

  17. Telophase 1 • All of the steps are same as mitosis except; • Whole chromosome is produced instead of one sister chromatid.

  18. Second Division of Meiosis • The second division of meiosis is completely the same as mitosis. • However at the end of Meiosis, 4 daughter cells each with half of the chromosome number of the original diploid cell are formed.

  19. Stages of Second Division Prophase 2 Metaphase 2 Anaphase 2 Telophase 2

  20. Animation of Meiosis http://www.cellsalive.com/meiosis.htm

  21. Questions • 5 differences between mitosis and meiosis

  22. Questions (a) (i)The diagrams show some of the stages of mitosis. Arrange the letters A - D to give the correct sequence of stages. Sequence D A C B

  23. (ii) Describe the role of the spindle in mitosis: It attaches centromeres and seperates the daughter chromatids. (b) Sexual reproduction involves the fusion of gametes. Explain the importance of meiosis in the life cycle of a sexually reproducing organism. Meiosis halves the chromosome number and increase the variation.

  24. References • Edexcel AS Biology, A Pearson Company, 2008, page 148,149,150,158,159 • Richard Llopis Garcia’s CD

  25. THE END

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