Meiosis 1: Prophase 1

Diagram of prohpase 1.

In prophase I the chromosomes become visible. However, unlike prophase of mitosis, the two chromosomes combine or synapse to form tetrads. Tetrads are also known as bivalents because they contain two pairs of chromosomes. At this point the chromosomes cross over at points called chiasmata. Crossing over allows the chromosomes to exchange genetic material, allowing for more different combinations of genetic material. As in the prophase of mitosis the nuclear envelope disperses, the spindle moves into the center, and the tetrads become connected to the spindle fibers by kinetochores.

Continue on to Meiosis 2: Metaphase 1

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