Essay on Meiosis : A First Step

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Meiosis is the process in which a diploid cell is divided into 4 haploid cells. Meiosis is separated into two parts meiosis I and meiosis II. In meiosis I, the first step is interphase and in this phase DNA is replicated. For example, in the diagram the DNA of big A, small a, big B, small b will all be replicated. This will create a doubling of the DNA that existed and will later be condensed into chromosomes. After interphase, prophase I occurs; in prophase I the replicated chromosomes pair up with their homologous pairs and this creates a tetrad that is formed by the sister chromatids. The sister chromatids were the homologous chromosomes before being paired up. In reference of the last example, the replicated big A will pair up with the original big A to form the tetrad. The big A and the replicated big A are now sister chromatids rather than homologous chromosomes. However, only when two chromosomes are paired up the chromosomes can be called sister chromatids. For example, big A and small a are not considered sister chromatids. During this step, a process named crossing over occurs. Crossing over creates genetic diversity among the chromosomes. This process is where two chromosomes exchange parts of their genetic information with each other. The region of exchange is called the chiasmata. For example, when big A and small a are paired up segments of small a can be exchanged with segments of big A. This also occurs with the big B and small b chromosomes. The next step is…

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