Phases of Meiosis

Phases of Meiosis - The spindle fibers attach to the...

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Phases of Meiosis Prophase I The events that occur during prophase of mitosis also occur during prophase I of meiosis. The chromosomes coil up, the nuclear membrane begins to disintegrate, and the centrosomes begin moving apart. Synapsis (joining) of homologous chromosomes produces tetrads (also called bivalents). The two chromosomes may exchange fragments by a process called crossing over . When the chromosomes partially separate in late prophase, the areas where crossing over occurred remain attached and are referred to as Chiasmata (sing. chiasma). They hold the chromosomes together until they separate during anaphase. Crossing over between homologous chromosomes is likely to occur at several different points, resulting in chromosomes that are mixtures of the original two chromosomes. One kinetochore forms on each chromosome instead of on each chromatid as in mitosis.
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Unformatted text preview: The spindle fibers attach to the chromosomes and begin to move them to the center of the cell as they do in mitosis. Metaphase I Bivalents (tetrads) become aligned in the center of the cell and are attached to spindle fibers. The chromosome alignment illustrated below is from a cell with a diploid chromosome number of 8. Independent assortment refers to the random arrangement of pairs of chromosomes. The diagram below shows four possible arrangements of chromosomes during metaphase 1 from an individual that has 6 total chromosomes. Suppose that the pink chromosomes are those that the individual inherited from its mother and the blue colored ones were inherited from its father. For each chromosome pair, the chromosome that is on the left (maternal or paternal) is determined randomly. As can be seen, there are several alignment possibilities....
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This note was uploaded on 12/15/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Phases of Meiosis - The spindle fibers attach to the...

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