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Cell Division

Cell Division . Mitosis and Meiosis. In Prokaryotes. The DNA is duplicated prior to cell division. In Prokaryotes. In most prokaryotes, the rest of the process of cell division is a simple matter of separating the contents of the cell into two parts. In Eukaryotes.

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Cell Division

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  1. Cell Division Mitosis and Meiosis

  2. In Prokaryotes • The DNA is duplicated prior to cell division

  3. In Prokaryotes • In most prokaryotes, the rest of the process of cell division is a simple matter of separating the contents of the cell into two parts.

  4. In Eukaryotes • In eukaryotes, cell division is more complex and occurs in two main stages. • The first stage, division of the cell nucleus, is called mitosis (my-TOH-sis). • The second stage, division of the cytoplasm, is called cytokinesis (sy-toh-kih-NEE-sis).

  5. Asexual Reproduction • Reproduction by mitosis is classified as asexual • since the cells produced by mitosis are genetically identical to the parent cell. • Mitosis is also the source of new cells when a multicellular organism grows and develops.

  6. Chromosomes • In eukaryotic cells, the genetic information that is passed on from one generation of cells to the next is carried by chromosomes. • Chromosomes are made up of DNA—which carries the cell's coded genetic information—and proteins.

  7. Chromosomes • The cells of every organism have a specific number of chromosomes. • Fruit flies have 8 chromosomes • Human cells have 46 chromosomes • Carrot cells have 18 chromosomes

  8. Chromosomes • Chromosomes are not visible in most cells except during cell division • At the beginning of cell division the chromosomes condense into compact, visible structures that can be seen through a light microscope.

  9. Chromosomes • Well before cell division, each chromosome is replicated, or copied. • Because of this, each chromosome consists of two identical “sister” chromatids (KROH-muh-tidz) • When the cell divides, the “sister” chromatids separate from each other. • One chromatid goes to each of the two new cells.

  10. Cell Cycle • Eukaryotes have separate periods of cell division with intervals of growth and protein synthesis. • This is represented as the Cell Cycle. • Interphase is the longest phase of the cycle, followed by cell division and cytokinesis.

  11. Interphase = Time between cells divisions. Normal Cell Functioning

  12. Early Prophase

  13. Prophase – DNA condenses into chromosomes Nuclear envenlope & nucleolus disintegrate, spindles appear Spindles attach to chromosome at centromere

  14. Metaphase- Spindles move chromosomes to cell equator

  15. Anaphase Spindles contract pulling chromosomes to opposite ends. Centromeres split to separate sister chromatids apart.

  16. Telophase Single stranded chromosomes stop moving & unwind. Nuclear envelope and nucleolus reappear. Spindles disintegrate.

  17. Chromosome Number • Most eukaryotes have two sets of chromosomes: one set from each parent. • Cells that have two sets of chromosomes are diploid (2n). • Cells with one set are haploid (n). • Thus diploid organisms have two copies of each chromosome. • These chromosome pairs are known as homologues or Homologous Chromosomes

  18. Karyotype = A photomicrograph of an individuals chromosomes Chromosomes are pasted with their homologous partner

  19. Sex Determination Females XX Males XY

  20. Sexual Reproduction = Meiosis • Gamete = sexual cells. EX: egg and sperm. Haploid in chromosome number • Somatic Cell = non sex cells always diploid. EX: skin, muscle, nerve, bone

  21. How do You get haploid gametes? • Meiosis = the process of nuclear division that reduces the number of Chromosomes in the original cell to the haploid number • Requires 2 cell divisions

  22. Meiosis 1 • Prophase 1 = Nuclear envelope and nucleolus disappear. Chromatin condenses into chromosomes. Chromosomes partner up into Homologous pairs. Crossing over of non sister chromosomes may occur to exchange genetic information

  23. Meiosis 1 continued • Metaphase 1 = Homologous chromosome pairs line up along the cell equator • Anaphase 1 = Homologous chromosome pairs split up and move as spindle fibers contract, toward opposite cell poles

  24. Meiosis 1 continued • Telophase 1 = chromosomes stop moving begin to unwind back into chromatin and nuclear envelope and nucleolus reform. • Cell splits into 2 daughter cells that must have further reduction of the chromosomes number.

  25. Meiosis 2 – Each daughter cell follows the path. • Prophase 2 = Nuclear envelope and nucleolus disappear. Chromosomes reform. • Metaphase 2 = CHromsomes line up along cell equator. • Anaphase 2 = Sister chromatids separate from each other.

  26. Meiosis 2 continued • Telophase 2= sister chromatids reach opposite poles of cell, unwind back into chromatin. Nuclear envelope and nucleolus reform. • Cytokinesis = Result in 4 non identicle , HAPLOID gametes.

  27. End Results of Mitosis versus Meiosis • Mitosis = 2 identical, DIPLOID, daughter cells • Meiosis = 4 non – identical , HAPLOID gametes

  28. Males vs Females • Males = spermatogenesis, 4 haploid • Females = oogenesis, results in 1 large haploid egg and 3 small polar bodies.

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