During the four phases of mitosis, nuclear division occurs in order for one cell to split into two. Additionally, we’ll mention three other intermediary stages (interphase, prometaphase, and cytokinesis) that play a role in mitosis. The centrosomes have replicated and are moving toward the poles.Īgain, the chromosomes are not yet attached to the spindle apparatus, which is growing outward from the centrosomes. The four stages of mitosis are known as prophase, metaphase, anaphase, telophase. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. DNA replication precedes the start of meiosis I. It is this step in meiosis that generates genetic diversity. If there was an interkinesis, then the nuclear envelopes begin to break down again during this stage. In meiosis I, chromosomes in a diploid cell resegregate, producing four haploid daughter cells. As Prophase 1 continues, the centrosomes move to opposite poles of the cell and spindle apparatus form. This process is important as it promotes genetic diversity. During the prophase I (PI) of meiosis, homologous chromosomes undergo pairing, synapsis, and meiotic recombination (1, 2). While they lined up, segments of the chromosomes may be exchanged. Each of the homologous chromosome line up side by side, forming tetrads. The polar body and the daughter cell both then enter meiosis II. During telophase I, the cytoplasm divides unequally, creating a larger daughter cell and a smaller polar body. During this stage of spermatogenesis, the cells are called secondary spermatocytes, or during oogenesis, secondary oocytes. Prophase 1 of meiosis is where the crossing-over occur. In egg cells, the female gametes, meiosis follows the same general phases with only a slight variation. As in prophase I, the chromosomes are condensed. Prophase II, the first step of meiosis II, begins with the two daughter cells produced by the first meiotic division (see figure right). Prophase II Note: Meiosis II is very similar to mitosis, except that during meiosis II only one member of each chromosome homolog pair is present, whereas in mitosis both are (it will help you remember this if you pronounce mitosis - only in your own mind! - as "my- TWO-sis"). Stages of Prophase Leptotene The chromosomes begin to condense and are attached to the nuclear membrane via their telomeres Zygotene Synapsis begins with. Moreover, the chromosomes in metaphase of mitosis can be a diploid set or haploid set, but the chromosomes in metaphase of meiosis II always consist of a.
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