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As you can see in the diagram above meiosis compromises of two divisions and within each of these divisions are four stages. I will now explain what happens within these two divisions of meiosis.
First division of meiosis...
Prophase 1-
During this stage the nuclear membrane breaks down and DNA is exchanged between homologous chromosomes. The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. At this stage, non-sister chromatids may cross-over.
Metaphase 1-
In the Metaphase, the centromere of each chromosome becomes attached to a spindle fibre. These spindle fibres pull the tetrads to the equator of the spindle and homologous chromosomes are lined up side by side as tetrads.
Anaphase 1-
During Anaphase in the first division of meiosis homologous pairs separate with sister chromatids remaining together. When the spindles shorten (and the continuous spindles slide past one another) the homologous pairs are separated. If each member of the pair is pulled to opposite ends of the cell no centromeres split. The cell elongates in preparation for division down the center.
Telophase 1-
The last meiotic division effectively ends when the chromosomes arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Sister chromatids remain attached during this stage and cells may enter a period of rest known as interkinesis.
Second division of meiosis...
(Gamete Formation)
Prophase 2-
In Prophase 2 the DNA does not replicate but the nucleoli and nuclear envelope disappears and the shortening and thickening of the chromatids occurs. Centrioles move to the Polar Regions and arrange spindle fibers for the second meiotic division.
Metaphase 2-
During this stage the chromosomes are pulled to the centre of the cell and align = randomly at the equatorial plate.
Anaphase 2-
The centromere of each chromosome splits and the sister chromatids by convention are now called sister chromosomes as they move toward opposing poles.
Telophase 2-
Here the nuclei re-form, the spindles break down, the cytoplasm divides and Cell division is complete. Four haploid daughter cells are obtained.
Both women and men have this process occurring within their bodies but the end result differs slightly. When meiosis occurs in a male the end result is four separate sperm cells which all develop and function correctly. However when meiosis occurs in a female the outcome is still four cells, egg cells this is, but only one of these eggs will develop. Not all four eggs are needed so the other three provide nutrients and food for the main egg that develops. Occasionally two eggs may develop but rarely any more.
