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Unit 10: C ell Division

Unit 10: C ell Division. Introduction. Bacteria replicate via binary fission. Eukaryotes replicate via a multi-stage life cycle including mitosis. Cell division includes a non-mitotic stage known as interphase, followed by mitosis and ended with cytokinesis. Interphase.

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Unit 10: C ell Division

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  1. Unit 10: Cell Division

  2. Introduction • Bacteria replicate via binary fission. • Eukaryotes replicate via a multi-stage life cycle including mitosis. • Cell division includes a non-mitotic stage known as interphase, followed by mitosis and ended with cytokinesis.

  3. Interphase • Prepares the cell for mitotic division. • Has 3 parts G₁, S and G₂ • Cells that are not destined to divide will spend the majority of their interphase in a stage known as G₀

  4. G₁: known as gap 1, is where the cell grows, enzymes and proteins needed for S stage are made. • S: known as synthesis, is when the chromosomes replicate . The result is the sister chromatins that look like a typical chromosome with the shape of an X joined by the centromere. • G2: synthesis of enzymes needed for cell division Centromere Sister chromatids

  5. Mitosis (M phase) • Mitosis is divided into several phases • Prophase (prometaphase included) • Metaphase • Anaphase • Telophase • Cytokinesis: rough division of cytoplasm at the end of cell division Overview Diploid 2n cell produces two 2n cells identical to the parent cell. Example: skin , liver, bone, etc. Diploid 2n 2n Diploid 2n

  6. Cell division in animal cells • Fertilization produces a diploid cell called zygote. • Zygote divides resulting in a ball of cells called a blastula. One cell of the blastula Whitefish blastula tissue

  7. Interphase • The animal cells in general appear round. The cell in interphase will have an intact nuclear membrane and the nucleoli are visible. nucleus Nucleoli

  8. Prophase • The cell in prophase will have beading DNA because chromatin is condensing into chromosomes. There is no arrangement of chromosomes. chromosomes

  9. Metaphase In metaphase the centromeres of chromosomes line up at the metaphase plate. metaphase plate

  10. Anaphase • The centromeres replicate and sister chromatids pull apart. Sister chromatids pulling apart

  11. Telophase The cell in telophase will have 2 collections of chromosomes because the sister chromatids are being pulled in opposite directions. The separated sister chromatids are then called daughter chromosomes. Two collections of chromosomes This stage marks the end of mitosis.

  12. Cytokinesis • A cleavage furrow forms to separate the cytoplasm of a cell. This cell shows cytokinesis overlapping with telophase. Cleavage furrow may start as early as anaphase

  13. Mitosis in plant cells • Occurs only in the meristem, which is actively growing and results in elongation of tips (stems and roots) and expansion of girth. • The cell cycle includes Interphase (G1, S, G2) and M phase (mitosis and cytokinesis). We will examine cells in interphase, mitosis (prophase, metaphase, anaphase, and telophase), and undergoing cytokinesis. Notice the nucleoli visible inside the nucleus nucleoli

  14. Prophase ‘Pro-’ means first, the nucleus shows lack of smoothness in color, due to the condensation of the chromosomes. There is no pattern of arrangement in the chromosomes. Chromosomes condensing Nucleoli may or may not be visible

  15. Metaphase • The prefix ‘meta-’ means middle. In metaphase the centromeres of chromosomes line up at the metaphase plate metaphase plate

  16. Anaphase • ‘Ana-’ means up, back. • The centromeres replicate and sister chromatids pull apart. • The cell in anaphase will have separating sister chromatids. Daughter chromosomes are separated sister chromatids Daughter chromosomes

  17. Telophase • ‘Telo-’ means end. • This stage marks the end of mitosis. • The cell in telophase will have 2 collections of chromosomes , which are now at opposite ends Collections of chromosomes

  18. Cytokinesis • Cytokinesis is not part of mitosis. It is the division of the cytoplasm and its content (except for the DNA). • It is an event that overlaps with the last part of mitosis. It can be seen as early as anaphase. Cell plate Cell plate

  19. Overview Animal Plant • Interphase • Prophase • Metaphase • Anaphase • Telophase /cytokinesis

  20. Meiosis: gametogenesis • Interphase • Precedes meiosis and is not a part of it. During it the chromosomes replicate. • Meiosis I • Consists of 4 sub stages • prophase I, metaphase I, anaphase I, and telophase I. • Cytokines • Is not a part of meiosis. • In humans, during cytokinesis the cytoplasm of sperm cells will be divided roughly in half but the cytoplasm of ova will be divided unequally, retaining most of the cytosol in one of the two daughter cells.

  21. Meiosis II Consists of 4 sub stages • prophase II, metaphase II, anaphase II, and telophase II. • Cytokinesis • Again, is not a part of meiosis. • The cytoplasm is divided a second time. • The final production is 4 sperm cells in males, and one ovum and 3 polar bodies in females.

  22. Meiosis Meiosis I: replicates and separates homologous chromosomes. Meiosis II: separates sister chromatids, producing gametes. Haploid n Haploid n Haploid n Haploid n Haploid n Haploid n Diploid 2n Meiosis I Meiosis II

  23. Crossing Over • Occurs in Prophase I. • Homologous chromosomes pair up and genetic material is exchanged. • The importance of crossing over is that generates genetic variation. Each one of these chromosomes will go to a different daughter cell to produce individual and unique gametes Sister chromatids Homologous crossing over genetic variation chromosomes

  24. Genetic variation • Genetic variation depends on how many different expressions a gene has. • A gene is located in a locus (plural loci). • A gene may have more than one expression. • color of eyes for example: black, brown, blue, green, just to name a few. • Each different form of expression is called an allele . Location of the gene in the locus A pair of homologous chromosomes will probably have different alleles of the same gene

  25. Meiosis Interphase Meiosis I Meiosis II n Homologous DNA replicates chromosomes (S stage) n n At the end, all 4 daughter cells carry unique DNA Because of crossing over the chromosomes are no longer the same as the originals n 2n 2n n NOTE: Meiosis is not proper only to humans, animals and plants produce gametes the same way. n

  26. Human Oogenesis Ovum Polar bodies Interphase (G₁, S, G₂) Notice this is the surface of the ovum Meiosis I Meiosis II

  27. Human Spermatogenesis Interphase (G1, S, G2) Meiosis I Meiosis II each one becomes a sperm The End

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