The chromatin condenses and undergoes a supercoiling so that the chromosomes shorten and thicken.
They can take up stains and be seen with a light microscope.
The chromosomes come together in their homologous pairs to form a bilvalent.
Each member of the pair has the same number of genes at the same loci.
Each pair consists of one maternal and one paternal chromosome.
The non sister chromatids wrap around each other and attatch at points called chaismata.
They may swap sections of chromatids with one another in a process called crossing over.
The nucleolus disappears and the nuclear envelope breaks down.
A spindle forms - made of protein microtubules.
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Meiosis 1 - Metaphase 1
Bivalents line up across the equator of the spindle, attached to spindle microtubules at the centromeres - The chaismata are still present.
The bivalents are arranged randomly (random assortment) with each member of a homologous pair facing opposite poles.
This allows the chromosomes to segregate independently when they are pulled apart in anaphase 1.
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Meiosis 1 - Anaphase 1
The homologous chromosomes in each bivalent are pulled by the spindle microtubules to opposite poles.
The centromeres do not divide (unlike Mitosis).
The chaismata seperate and lengths of chromatid that have been crossed over remain with the chromatid to which they have become newly attached.
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Meiosis 1 - Telophase 1
For most animal cells, nuclear envelopes form around each set of 23 chromosomes and the cell is divided by Cytokinesis. The chromosomes then uncoil and there is a short Interphase.
However in most plant cells, there is no Telophase 1, the plant cell goes straight into Anaphase 1 and Meiosis 2.
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Meiosis 2 - Prophase 2
If a nuclear envelope has reformed, it breaks down again.
The nucleolus dissappears, chromosomes supercoil and spindle forms.
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Meiosis 2 - Metaphase 2
The chromosomes arrange themselves on the equator ofthe spindle. They are attached to the spindle microtubules at the centromere.
The chromatids of each chromosome are randomly assorted.
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Meiosis 2 - Anaphase 2
The centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres.
The chromatids randomly segregate - become daughter chromosomes.
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Meiosis 2 - Telophase 2
Nuclear envelope reforms around the haploid daughter nuclei.
In animals, the 2 cells now divide to give 4 haploid cells (cytokinesis).
In plants, a tetrad of 4 haploid cells is formed (no cytokinesis).
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