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Meiosis How to make SEX cells!
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What is Meiosis? Most living things have body cells and sex cells (sperm and eggs) Eggs are female sex cells Sperm are male sex cells Meiosis is a special cell division that results in sex cells
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What’s the Big Picture? In meiosis, a cell divides twice making a total of how many cells? 4
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What’s the Big Picture? 1st time, each chromosome in a pair move away from its partner, each chromosome goes to a different cell, sister chromatids stay joined together 2nd division – sister chromatids separate
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Some Terms: Cells that have the normal number of chromosomes are called “Diploid” Cells that have ½ the normal number of chromosomes are called “Haploid” Meiosis results in 4 Haploid cells that are genetically different from each other (and remember the parent cell was diploid)
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Some Terms: Cells have pairs of chromosomes each chromosome in a pair is “homologous” to the other (they are homologs). In meiosis the homologous chromosomes separate.
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Interphase I DNA Replicates
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PROPHASE 1 Nuclear membrane begins to break down
Centrioles begin to move away from each other Homologous (matching) chromosomes come together to form “tetrads” (remember: each chromosome has 2 strands of sister chromatids – now looks like 4 strands)
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Metaphase 1 Sister chromatids become attached to fibers
Homologous chromosomes move to the center of the cell
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Anaphase 1 Tetrads separate into double stranded chromosomes
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Telophase 1 Cell membrane pinches cell into two
Nuclear membrane does not reform
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Interphase II DNA DOES NOT Replicate
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Prophase II (2) Centrioles double and form fibers again
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Metaphase II (2) Fibers connect chromatids and they line up at the middle
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Anaphase II (2) Fibers pull each strand apart to opposite ends of the cell
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Telophase II (2) Cells Divide – Now have 4 cells
Each has ½ the # of Chromososmes (Haploid) Each is genetically different from the others Nuclear membrane reforms Cell pinches off
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The Whole Thing Part 1…
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The Whole Thing Part 2…
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