Reproduction the Process of Meiosis

DNA replication occurs prior to meiosis, so a cell’s chromosomes are duplicated the time meiosis I begin: Each chromosome consists of two sister chromatids. The nucleus is diploid (2n). It contains two sets if chromosomes, one from each parent. Let us now turn to the cellular events that occur during meiosis itself.

The first stage of meiosis 1 is prophase 1. During this phrase, the chromosomes condense, and homologous chromosomes align tightly and swap segments more about segment swapping in the next section. The centrosome gets duplicated along with its two centrioles. One centriole pair moves to the opposite side of the cell as the nuclear envelope breaks up. Spindle microtubules; begin to extend from the centrosomes.

By the end of prophase 1, microtubules of the spindle connect the chromosomes to spindle poles. Each chromosome is now attached to one spindle pole, and its homologous partner is attached to the other. The microtubules lengthen and shorten, pushing and pulling the chromosomes as they do. At metaphase I, all of the microtubules are the same length, and the chromosomes are aligned midway between the poles of the spindle.

In anaphase I, the spindle microtubules separate the homologous chromosomes and pull them toward opposite spindle poles. During telophase I, the chromosomes reach the spindle poles. New nuclear envelopes form around the two clusters of chromosomes as the DNA loosens up. Each of the two haploid (n) nuclei that form contains one set if duplicated chromosomes. The cytoplasm may divide at this point to form two haploid cells. Interphase occurs in some cells at the end of meiosis I, but the DNA is not replicated before meiosis II begins.

Meiosis II During prophase II, the chromosomes condense as a new spindle forms. One centriole moves to the opposite side of each new nucleus, and the nuclear envelopes break up. By the end of prophase II, microtubules connect the chromosomes to the spindle poles. Each...