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Biology

Biology. The Cellular Basis of Inheritance. Why Do Cells Divide?. Cell Division is the splitting of a single cell into 2 cells . 3 life processes occur: Growth : this is the increase of cell in size . Differentiation is the specialization in cells .

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Biology

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  1. Biology The Cellular Basis of Inheritance

  2. Why Do Cells Divide? Cell Divisionis the splitting of a single cell into 2 cells. 3 life processes occur: • Growth: this is the increase of cell in size. • Differentiationis the specialization in cells. • Repair: this is the ability of an organism to fix itself; humans repair their skin blood vessels and bone. • Regenerationis the ability of an organism to replace a missing body part (like a starfish regrowing an arm). http://beckstrom.com/images/d/d1/SpottedLinkiaRegenerating.jpg

  3. Reproduction: When an organism is single-celled and that cell divides, it is reproducing. This is a form ofasexual reproduction. • Bacteria and unicellular eukaryotesreproduce this way. • The arm that broke off from the starfish can also reproduce asexually by cell division. It slowly regrows a new body. • Asexual reproduction produces genetically identical offspring to the parents. http://www.google.com/imgres

  4. Sexual Reproduction: • Sexual reproductionproduces genetic varieties in offspring. • Plants and animals reproduce this way. This results in a recombination of chromosomes through meiosis, a specialized form of cell division. http://www.google.com/imgres

  5. How Do Cells Divide? • The cell cycleis the sequence of phases in the life cycle of the cell • The cell cycle has 2 parts:Interphase (Growth and preparation) and Cell Division • Cell Division includes: Mitosis(nuclear division) and Cytokinesis(cytoplasm division). http://www.google.com/imgres

  6. Some Terms: • Chromatin is the fibrous form of DNA and proteins that make up chromosomes. • This is what is found within the nucleus of the cell during interphase. • It is clumped DNA. • Once chromosomes have been replicated, they are paired together in the form of sister chromatids. • These are identical structures that are side by side. • Sister chromatids are held together by a centromere. • This is the point of attachment.

  7. https://eapbiofield.wikispaces.com/file/view/centromere.gif

  8. Cell Division: Interphase: • G1, or gap 1, is characterized by growth and development. • S stage, or Synthesis, is when the chromosomes are replicated. • G2, or gap 2, is when the cell synthesizes organelles and other materials. • This is the longest phase of the entire cell cycle. The cell is in preparation for the nucleus to divide.

  9. http://www.ivy-rose.co.uk/Topics/Cell_Structures/Cell-Cycle_cIvyRose.jpghttp://www.ivy-rose.co.uk/Topics/Cell_Structures/Cell-Cycle_cIvyRose.jpg

  10. Mitosisis the formation of 2 nuclei from 1. It occurs in 4 stages. 1. Prophase: • Chromosomes condense & become visible under the light microscope • Microtubules from the mitotic spindles • The nuclear envelope & nucleolus break apart & disappear • Centromeres attach to the spindle fibers 2. Metaphase: • The chromosomes move to the center of the cell • The center of the cell is called themetaphase plate

  11. Prophase: Metaphase: http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/images/metaphase1_ac.jpg http://web.grcc.edu/biosci/pictdata/mitosis/prophase.jpg http://www.lima.ohio-state.edu/biology/images/metaphase.jpg http://web.grcc.edu/biosci/pictdata/mitosis/prophase.jpg

  12. 3. Anaphase: • Centromeres divide & the spindle fibers pull 1 set of sister chromatids toward opposite poles • Once chromosomes are at opposite poles, anaphase is over http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/mitosis/whitefish_mitosis_anaphaseX400.jpg http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/images/early_anaphase1_pc.jpg

  13. 4. Telophase: • A nuclear envelope forms around each set of chromosomes • Chromosomes uncoil into chromatin • Mitotic spindle fibers disassemble http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Laboratory/Mitosis/Photographs/whitefish_mitosis_telophaseX400.jpg http://www.grossmont.edu/cmilgrim/Bio220/BIO221/AlliumMitosis/telophase.jpg

  14. Cytokinesis: • This is a.k.a.cytoplasm separation • In animal cells, this begins in telophase as the nuclei reform. • This starts at the center of the cell and pinches inward.This is called acleavage furrow. • In plant cells, this begins in anaphase and starts in the center of the cell along the metaphase plateand grows outward. • This is called thecell plate.

  15. http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.12.9cytokinesis.jpghttp://fig.cox.miami.edu/~cmallery/150/mitosis/c7.12.9cytokinesis.jpg

  16. Cancer • Tumors: masses/clusters of cells • Benign: non-cancerous • Malignant: cancerous (usually uncontrolled dividing cells) http://www.google.com/imgres

  17. Metastasis: spreading of cancerous cells • Treatment:surgery (removes tumor), radiation & chemotherapy (destroys cells by disrupting cell cycle) • Radiation & chemo side effects:healthy cells may die, sterility, hair loss, nausea

  18. What is Meiosis? Remember that humans have 46 chromosomes (or 23 pairs) in their cells. • This means they have 2 complete sets of chromosomes. • Diploid, or 2n, is a cell that has 2 complete sets of chromosomes (in humans, 46). • Haploid, or 1n or n, is a cell that has only 1 set of chromosomes (in humans, 23). http://www.google.com/imgres

  19. Human’s sex cells, orgametes, are haploid. • All human body cells are produced through mitosis whereas the sex cells, or gametes, are produced through meiosis. • Gametes aresperm and eggand have only 23 chromosomes in each. • When they fuse (at fertilization), they form azygote (23 + 23= 46). • This is how each generation remains stable.

  20. Meiosis is a type of cellular reproduction in which the # of chromosomes are reduced by ½ so that the daughter cells are haploid (n). • Homologous pairsare pairs of chromosomes. • Each of the 23 chromosomes has a matching chromosome (with 1 exception: the sex chromosomes). • Sex chromosomesare X and Y. http://www.google.com/imgres

  21. The Phases of Meiosis: • Prior to meiosis, a diploid cell replicates its chromosomes (Interphase). • Meiosis has 2 stages:Meiosis I and Meiosis II.Each has 4 phases.

  22. Homologous Chromosomes: http://silverfalls.k12.or.us/staff/read_shari/homologouschrom.jpg http://www.treachercollins.co.uk/gene/chrom.gif Karyotype: display of chromosomes in # order; informs chromosomal # abnormality, chromosomal abnormaility & genetic sex

  23. Meiosis I: • Prophase I:chromosomes condense, homologous chromosomes become attached to each other, each homologous chromosome contains 4 sister chromatid (this is called a tetrad, meaning 4). • Metaphase I:homologous pairs align along the middle of the cell. • Anaphase I:homologous pairs split. 4. Telophase I and Cytokinesis:Nuclei reform and the cells split. This result is 2 diploid cells, each with 2 complete sets of chromosomes.

  24. http://www.google.com/imgres

  25. Meiosis II: • Prophase II:Spindle fibers form again & chromosomes condense. NO tetrads; NO crossing over! • Metaphase II:chromatids move to the center of the cell. • Anaphase II:chromatids are pulled to opposite poles. • Telophase II and Cytokinesis:Nuclei reform and cells separate. The result is 4 haploid cells.

  26. http://www.google.com/imgres

  27. Meiosis I  Meiosis II  http://www.accessexcellence.org/RC/VL/GG/images/meiosis.gif

  28. In human males, 4 haploid cells result (sperm cells) but in human females, only 1 of the 4 haploid cells forms an egg cell. The other 3 receive no cytoplasm and do not form gametes (they disintegrate). • Interphase occurs only ONCE (Meiosis I), meaning chromosomes replicate only 1X.

  29. What are the differences between mitosis and meiosis? • Meiosis produces daughter cells with ½ the # of chromosomes (haploid cells), mitosis produces diploid cells. • Meiosis produces daughter cells that are NOT genetically identical to each other (the homologous chromosomes separation is random); mitosis produces EXACT copies of parent cells. • Meiosis produces 4 haploid cells; mitosis produces 1 cell.

  30. Genetic Variation Variationresults from the recombination of DNA (from meiosis & fertilization) and accounts for the differences between members of a population. Sources of Genetic Variation: • Random separation of homologous pairs of chromosomes • Random combination of haploid gametes • Crossing Over(tips of homologous chromosomes switch places) occurs during prophase I (meiosis I)

  31. http://kvhs.nbed.nb.ca/gallant/biology/mitosis_meiosis.jpg

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