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the process of meiosis

Would someone be able to explain the process of meisois to me in a relatively simple way that I will be able to understand. Becasue i really dont understand it.
Thank-you heaps in advanced. :smile:

Reply 1

MadNatSci

Hmm, this is always a tricky one to explain so apologies if I don't explain it well, but I will try! I'm assuming this is GCSE level but if it's more advanced, let me know!

Meiosis is a form of cell division that makes gametes, and the first thing to be clear about is that gametes have half as much DNA as normal ('somatic') cells. So at the end of meiosis, if you started with one cell, you will have four daughter cells that each have half as much DNA as the original cell. Is that as clear as mud?! Hopefully it will become clearer as I explain...

The first thing that happens is that the DNA in the original cell is duplicated. So where you had 46 chromosomes (assuming this is a human cell) you now have 46 pairs of chromatids - and within each chromatid pair the two partners are identical. The next bit is similar to mitosis in that the chromatids all assemble at the centre of the cells (its 'equator'), but here the similarity ends. Remember that although you have 46 chromosomes (by this point pairs of chromatids), half of them are from your mother and half are from your father, and so you have homologous pairs of chromosomes - they aren't the same, but they are equivalent. Each member of these homologous pairs wraps round its partner and they often swap bits of genetic material - this is called crossing over.

The next step is the separation of the homologous chromosomes from one another: they're pulled apart by microtubules. This is a crucial difference from mitosis. In mitosis, the chromatids are separated from each other, but in meiosis each pair of chromatids is separated (intact and still joined to its *identical* mate) from its partner pair. Once the chromatid pairs have reached opposite ends of the cell, it divides into two. This is the end of the first part of meiosis, called 'meiosis 1'.

So at the end of meiosis 1 you have two cells, each of which has 23 pairs of chromatids, and each chromatid is physically joined to its identical partner. The next bit of meiosis is a lot easier to understand because it's basically the same as mitosis. The chromatid pairs line up at the equator and are pulled apart by microtubules, in each cell, so you get four progeny cells each with 23 chromosomes - ie half as many as the original cell (which had 23 pairs of chromosomes, the pairs consisting of a maternal chromosome and a paternal chromosome).

Does this make any sense at all? I've tried to explain it as clearly as I can but it's a very difficult topic to explain and I have almost certainly said some stuff that isn't clear - please do ask me questions and I'll explain whatever isn't clear! Also very sorry if this post sounds patronising but I'm trying my hardest to be absolutely clear and precise! :redface: