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Meiosis produce haploid cells, twice. How?

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Meiosis produce haploid cells, twice. How?

Postby easternuser » Wed Oct 05, 2011 6:58 pm

From what I know,
Meiosis has two stages.
Meiosis I produces two haploid daughter cells. Meiosis one is preceded by interphase.
Meiosis II also produces two haploid cells, but does not undergo interphase, and it is an immediate continuation of meiosis I.

So,
How can the diploid cell be halved it's chromosomal number, twice and still be haploid? Shouldn't it be quarter-ploid or something?
Thanks, for your input :)
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Postby Cat » Fri Oct 07, 2011 5:09 pm

"Meiosis has two stages.
Meiosis I produces two haploid daughter cells. Meiosis one is preceded by interphase.
Meiosis II also produces two haploid cells, but does not undergo interphase, and it is an immediate continuation of meiosis I."

No, no, no!

1. Interphase - double genome - makes cell quadroploid (4 copies of everything)
2. recombination
3. meiosis 1: cell division - 2 diploid daughter cells
4. meiosis 2: cell division of 2 cells - 4 haploid daughter cells
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Re: Meiosis produce haploid cells, twice. How?

Postby organism » Wed Oct 19, 2011 9:13 pm

no no no no no no

A diploid cell is in interphase and doubles it's DNA to make chromosomes with two chromatids(sister chromatids).

When it enters meiosis 1 the homologous chromosomes get separated and each chromosome of the homologous pair goes to a new cell. So in meiosis 1 you get two haploid cells which have chromosomes with two chromatids.

When meiosis 1 is finished the two cells go into a short interphase and after that they enter meiosis 2. So when the 2 cells enter meiosis 2 they are haploid and have chromosomes with two sister chromatids. During meiosis 2 the 2 sister chromatids on each chromosome split and you get 4 cells that are haploid.

So in meiosis 1 one diploid cell divides to make 2 haploid cells and in meiosis 2 the cells make copies of themselves so meiosis 2 is basically the same as mitosis.
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Re: Meiosis produce haploid cells, twice. How?

Postby aptitude » Fri Oct 21, 2011 3:50 am

organism wrote:no no no no no no

A diploid cell is in interphase and doubles it's DNA to make chromosomes with two chromatids(sister chromatids).

When it enters meiosis 1 the homologous chromosomes get separated and each chromosome of the homologous pair goes to a new cell. So in meiosis 1 you get two haploid cells which have chromosomes with two chromatids.

When meiosis 1 is finished the two cells go into a short interphase and after that they enter meiosis 2. So when the 2 cells enter meiosis 2 they are haploid and have chromosomes with two sister chromatids. During meiosis 2 the 2 sister chromatids on each chromosome split and you get 4 cells that are haploid.

So in meiosis 1 one diploid cell divides to make 2 haploid cells and in meiosis 2 the cells make copies of themselves so meiosis 2 is basically the same as mitosis.


yes yes yes yes yes :D

This is why meiosis I is considered "reductional division", because it reduces from diploid to haploid, and meiosis II is considered "equational division".
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Re: Meiosis produce haploid cells, twice. How?

Postby angusrose » Mon Oct 24, 2011 11:12 am

I think this highlights a common problem that stems from a misunderstanding of what form the chromosomes take during the cell cycle. When not dividing (G1 of interphase, or when the cell leaves the cell cycle) the cell's chromosomes exists as SINGLE strands of DNA. So, in a human cell there would be 46 single strands of DNA. Following S phase of interphase, the amount of DNA doubles as DNA replication has just occurred. At this point, the cell's chromosomes take on the appearance of an X, which is what most people think a chromosome looks like all the time - not the case! It looks like this because the DNA that makes up the chromosome has replicated, and the copy strand is still attached to the original strand by the kinetochore. The chromosome remains in this form until anaphase of mitosis or anaphase II of mitosis at which point the spindle apparatus pulls the replicated chromosome apart forming 2 new chromosomes, each of which is destined for the new cell being created by the division.

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