Figure 8-2. Meiosis.

Figure 8-2Meiosis

A premeiotic germ cell has two copies of each chromosome (2n), one maternal and one paternal. Chromosomes are replicated during the S phase, giving a 4n chromosomal complement. During the first meiotic division, each replicated chromosome (actually two sister chromatids) aligns at the cell equator, paired with its homologous partner; this pairing off, referred to as synapsis, permits genetic recombination (discussed later). One homolog (both sister chromatids) of each morphologic type goes into one daughter cell, and the other homolog goes into the other cell. The resulting 2n cells undergo a second division without intervening DNA replication. During this second meiotic division, the sister chromatids of each morphologic type separate and these now independent chromosomes are randomly apportioned to the daughter cells. Thus, each diploid cell that undergoes meiosis produces four haploid cells, whereas each diploid cell that undergoes mitosis produces two diploid cells (see Figure 1-10).

From: Section 8.1, Mutations: Types and Causes

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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