Meiosis II

Meiosis, nuclear division that forms haploid cells, consists of two main stages: meiosis I and meiosis II.

During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes.

Prophase II (a)

If the chromosomes decondensed in telophase I, they condense again. If nuclear envelopes were formed, they fragment into vesicles. The centrosomes that were duplicated during interkinesis move away from each other toward opposite poles, and new spindles are formed.

Prometaphase II

The nuclear envelopes are completely broken down, and the spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.

Metaphase II (b)

The sister chromatids are maximally condensed and aligned at the equator of the cell.

Anaphase II (c)

The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell.

Telophase II and Cytokinesis (d)

The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover.

Image A shows a cell in the stage of prophase two. Image b shows a cell in metaphase two, where the chromatids are aligned in the center of the cell. Image c shows a cell in anaphase two, where the chromatids are pulled apart and arranged at opposite poles in the cell. Image d shows a cell in telophase two and cytokinesis. The chromatids have arrived at opposite poles and have begun to decondense and the cell is almost separated into four unique haploid cells.

Figure 1. Meiosis II.

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