Meiosis vs Mitosis

[mmy322]

what are the benefits from the 2 diff ways that homologous chromosomes are positioned at metaphase in meiosis & mitosis?

[Blahah]

Well, metaphase occurs twice in meiosis and once in mitosis. The difference is between metaphase of mitosis and metaphase I of meiosis - metaphase II of meiosis is pretty similar to metaphase of mitosis.

 

If you think about what's being achieved by the process, you can see how the different positionings are beneficial to the process. In mitosis (and metaphase II of meiosis) the chromosomes are separated into two sister chromatids to create the haploid daughter cells. To achieve this, the chromosomes are lined up approximately along the centre of the cell and then pulled apart by the contracting microtubules...

 

 

In metaphase I of meiosis, pairs of homologous chromosomes, having just completed crossing over, are being pulled apart. So instead of pulling the chromatids of one chromosome apart, you are pulling two chromosomes apart from one another. For this reason, the pairs of chromosomes line up roughly along the axis, but this time with one chromosome either side of the central line.

So you can see the difference: mitosis and metaphase II are pulling single chromosomes apart to separate the sister chromatids; metaphase I is pulling pairs of chromosomes apart to separate the chromosomes.