Lecture 2- mitosis and meiosis

Lecture 2- mitosis and meiosis - Cell Division: Mitosis and...

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Cell Division: Mitosis and Meiosis So to review: cells have to divide up their contents so that each daughter cell has everything it needs to survive. In the case of the chromosomes, this is an exacting task because you have to get exactly one copy of each chromosome (including one copy of each of the two homologous chromosomes) into each daughter cell. The first thing the cell has to do is make sure that it duplicates the DNA once before it divides. It does this by having a ordered series of steps, the cell cycle, controlled by checkpoints that make sure the cell is ready to move on to the next step. Mitosis O.K., but how do cells divide up the chromosomes equally? The answer is a process that you can (and hopefully will) watch called mitosis . It seems rather complicated when you first study it but, considering the difficult task of dividing up the chromosomes that mitosis must accomplish, it is extraordinarily elegant. These are some events you need to know:
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G2 replication of the centrosome (and centrioles in some cases). Prophase Centrosomes move to the poles Spindle forms Chromosome condensation – chromatids become evident (remember that each chromatid is actually a chromosome even though we refer to the pair of chromatids as a "mitotic chromosome") Kinetochores form Prometaphase Nuclear envelope breakdown Polar microtubules and kinetochore microtubules form Chromosomes arrive on metaphase plate Metaphase Chromosomes are lined up on the metaphase plate Sister chromatids bound to kinetochore microtubule on opposite spindles Anaphase Centromeres separate Kinetochore microtubules shorten
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Spindle elongates Telophase Spindle breaks down Chromosomes decondense Nucleus reforms The trick with getting the chromosomes to separate evenly is to get them lined up on the metaphase plate. Ingredients for a metaphase mitotic spindle: 1) Keep the chromatids paired until it is time to segregate. 2)
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Lecture 2- mitosis and meiosis - Cell Division: Mitosis and...

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