Meiosis

[Trouble]

Can someone please explain this? Is it like Mitosis except x2? I'm assuming this because you get 4 sex cells rather than 2 cells and the 4 sex cells have 1/4 of the chromosomes of the original parent cell.

[Zwitterion]

Meiosis:

One cell.
Genetic information inside cell doubles as in mitosis.
Cell splits. (Up until this point mitosis and meiosis are the same)
Cell splits again.

Each cell (now a haploid cell) contains half of the genes one regular cell would have. This is so that the number of chromosomes is restored when two gametes fuse to become the zygote. In mitosis the cell only divides once which leaves you with two identical diploid cells. In meiosis each daughter cell divides once more leaving you with four haploid cells.

Image (courtesy of Wikipedia):



EDIT: This is important. Gametes do not have 1/4 of the original cell's genes. They have half. Cells have to replicate their genetic information (and other things such as organelles) before they can divide resulting in one cell having twice the information as normal. When it divides, each cell gets a full set of the information. In meiosis there is another division resulting in half of the original information.

[helpful_harry]

Mitosis happens and this is the first stage.
Then the similar sort of cell division happens but with no chromosomal replication so the daughter cells have only half the amount of DNA as a normal cell (known as haploid for half and diploid for full number of chromosomes).

[Trouble]

U.S. NAVY, no comments?

[Justin.]

Someone can just read the threads if they wish, they don't have to reply just because they entered the thread. I'm not saying he is not going to post, just don't expect everyone to reply.

[U.S.-NAVY]

Originally Posted by Trouble

U.S. NAVY, no comments?

Ha. There's not much to say.

Basically a diploid cell replicates its genetic material And undergoes meiosis I. Meiosis I is actually pretty different to mitosis. In Meiosis I you have a replicated diploid cell turning into a haploid cell with chromosomes rather than chromatids. There is crossing over at some points before Meiosis I which makes for some genetic variability in offspring. You then have two haploid cells. Then Meiosis II happens. Meiosis II differs from mitosis primarily in the conspicuous absence of genetic replication. Thus, from Meiosis II you end up with four haploid cells.

Basically it goes

2n > 2x(2n) > 2x(n) > n

For each cell. Note that 2x(2n) does not represent any type of quadraploidy, simply replicated diploid. Just as 2x(n) does not represent diploid, but replicated haploid.

For the whole thing you go

1 Cell, 2n > Replication > 1 Cell, 2x(2n) > Meiosis I > 2 Cells, each 2x(n) > Meiosis II > 4 Cells, each n

[Trouble]

Ahhhh I see now. Yeah, you explain it pretty well, so I was just waiting for your answer