Introduction to Mitosis Prophase and Prometaphase As we discussed in cell cycle , before cells are allowed to enter M phase they must meet certain cellular requirements. Among these requirements are appropriate cell size and cellular environment. Following DNA replication in S phase, cells contain twice their normal number of chromosomes. Because cells that undergo mitosis are diploid, their number of chromosomes can be represented as 2 N, where N equals the number of distinct chromosomes in the cell. Cells about to enter M phase, which have passed through S phase and replicated their DNA, have 4 N chromosomes. Entry into M phase is allowed by the formation of the mitotic cyclin-Cdk complex known as M phase-promoting factor that occurs as a cell cycle regulatory mechanism in the G2 phase . The first phase of mitosis within M phase is called prophase. It follows G2, the final phase of interphase. A cell entering M phase manifests a number of physicsl signs. Among these are condensation, or thickening, of chromosomes. Chromosome condensation is visible through a
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This note was uploaded on 01/27/2012 for the course BIOLOGY BSC1005 taught by Professor Rodriguez during the Winter '09 term at Broward College.