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Cell Division

Cell Division. Mitosis and Meiosis. Recall A Few Main Things. All new cells come from existing cells DNA is stored in the nucleus of cells in eukaryotes. Chromosomes. A chromosome is a single, very long, strand of DNA Each chromosome contains many thousands of genes. Diploidy.

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Cell Division

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  1. Cell Division Mitosis and Meiosis

  2. Recall A Few Main Things • All new cells come from existing cells • DNA is stored in the nucleus of cells in eukaryotes

  3. Chromosomes • A chromosome is a single, very long, strand of DNA • Each chromosome contains many thousands of genes

  4. Diploidy • Each species has a set # of chromosomes • We also have 2 versions of each chromosome (called homologous chromosomes) • I.e. humans have 23 sets of chromosomes, or 46 total

  5. Types of Cell Division • Usually when we make new cells, we want them to be identical to existing cells • i.e. make new skin cells from existing ones • The new cell is completely identical

  6. Mitosis • Cell division that creates identical daughter cells • So the new cell has the exact same chromosomes as the original cell

  7. The Extent of Mitosis • Almost every single cell in our body is made from mitosis • Exceptions: the first cell, sperm/egg cells • When we grow new skin, new hair, new muscles – all of that is mitosis • So every cell in our body has the exact same set of chromosomes

  8. Sperm/Egg • You pass on half your genes to offspring • You must make a gamete (sperm or egg cell) with half of your chromosomes • Each gamete randomly receives 1 of the 2 versions of each chromosome

  9. Meiosis • Each parent cell produces 4 daughter cells • Each daughter cell has 1 set of chromosomes (half of the parent’s chromosomes) • (is haploid)

  10. # of Possible Gametes • There are 223 possible chromosome combinations to make a gamete • =8,388,608 possibilities • So you are 1 out of 8,388,6082 possibilities • You are quite literally 1 in a trillion (1 of 70,368,744,200,000 possible combinations of your parents)

  11. Mitosis Meiosis • Identical offspring (same set of chromosomes) • 2 daughter cells • Creates all body cells • Produces diploid cells • Offspring have half as many chromosomes • 4 daughter cells • Creates sperm/egg • Produces haploid cells Mitosis vs. Meiosis

  12. What’s the Point? • Meiosis allows us to have offspring that are different and have a unique combination of genes • This increases diversity in the population • Increased diversity means increased ability for the species to survive and adapt to new situations

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