Mitosis and Meiosis Help! Watch

Nator
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Hey guys, I was just wondering does interphase double the chrosome number from 46 to 92 due to DNA replication?
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SteveCrain
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It doesn't double the chromosome number, but it doubles the amount of DNA. Chromosomes usually look like chromatids, but because you only see them in prophase, you see them with twice the amount of DNA. There are the same number of chromosomes, as the number of centromeres does not increase.
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Nator
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(Original post by SteveCrain)
It doesn't double the chromosome number, but it doubles the amount of DNA. Chromosomes usually look like chromatids, but because you only see them in prophase, you see them with twice the amount of DNA. There are the same number of chromosomes, as the number of centromeres does not increase.
Thanks! And you know that meiosis has 2 divisions, how many chromosomes does each cell contain at the first division where the cell divides into 2 cells? I know at the second division that the 4 cells each contain 23 chromosomes but how many does each of the 2 cells contain at the first division? Thanks
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wasting-time
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46
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Nator
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(Original post by tgarrud)
46
But how can it go from 46 to 46 to 23? How can it divide in way that maintains the same no. of chromosomes after a division into 2 cells?
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ScienceGeek3
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I just made a thread about a similar question!! At the end of the second division.. four cells are produced right? Do each of these 4 cells contain one chromatid or one chromosome, so confused :/
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SteveCrain
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(Original post by Nator)
Thanks! And you know that meiosis has 2 divisions, how many chromosomes does each cell contain at the first division where the cell divides into 2 cells? I know at the second division that the 4 cells each contain 23 chromosomes but how many does each of the 2 cells contain at the first division? Thanks
It contains 46 chromosomes. It divides to give 23 chromosomes in meiosis 1. This then divides again to give 23 chromosomes.

The original DNA has been replicated before division. The reason you think a chromosome lookes like and "X" rather than an "l" is because you only see them during mitosis when they are dividing.

DNA replicates during Interphase, which is before nuclear division (nuclear division= meiosis and mitosis)

But they are still called a single chromosome, because a) the two strands are exactly the same and b) they are attached to a single centromere.
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SteveCrain
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(Original post by ScienceGeek3)
I just made a thread about a similar question!! At the end of the second division.. four cells are produced right? Do each of these 4 cells contain one chromatid or one chromosome, so confused :/
1 chromosome
. See above, I've tried to explain
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Nator
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(Original post by SteveCrain)
It contains 46 chromosomes. It divides to give 23 chromosomes in meiosis 1. This then divides again to give 23 chromosomes.

The original DNA has been replicated before division. The reason you think a chromosome lookes like and "X" rather than an "l" is because you only see them during mitosis when they are dividing.

DNA replicates during Interphase, which is before nuclear division (nuclear division= meiosis and mitosis)

But they are still called a single chromosome, because a) the two strands are exactly the same and b) they are attached to a single centromere.
So it starts with 46, then divides to give 2 cells of 23 each, then those divide to give 4 cells of 23?
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Elwyn
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(Original post by Nator)
So it starts with 46, then divides to give 2 cells of 23 each, then those divide to give 4 cells of 23?
Yes, it goes: Diploid (2n) -> 2x Haploid (n) -> 4x Haploid (n)

Have a look at this video, I find it amazingly helpful: http://www.youtube.com/watch?v=ijLc52LmFQg
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Nator
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(Original post by Elwyn)
Yes, it goes: Diploid (2n) -> 2x Haploid (n) -> 4x Haploid (n)

Have a look at this video, I find it amazingly helpful: http://www.youtube.com/watch?v=ijLc52LmFQg
Thanks a lot mate!
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wasting-time
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(Original post by Nator)
But how can it go from 46 to 46 to 23? How can it divide in way that maintains the same no. of chromosomes after a division into 2 cells?
the cell goes through normal interphase and chromosones are copied and are visible as sister chromoatids.
.
pairs of homologous chromosones pair up and seperate in meiosis 1
chromotids are seperated in meiosis 2.
as shown in this diagram:



so to answer your question it goes 2N -> 2N -> N -> N because after interpahse the chromosones are sister chromatids (the have replicated) but they are still joined so you still only count them as 1 chromosone so when meiosis 1 happens the chromosone number is halved. so sorry i said 46 but its actually 23 as the homologous chromosones have seperated.
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Nator
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(Original post by tgarrud)
the cell goes through normal interphase and chromosones are copied and are visible as sister chromoatids.
.
pairs of homologous chromosones pair up and seperate in meiosis 1
chromotids are seperated in meiosis 2.
as shown in this diagram:



so to answer your question it goes 2N -> 2N -> N -> N because after interpahse the chromosones are sister chromatids (the have replicated) but they are still joined so you still only count them as 1 chromosone so when meiosis 1 happens the chromosone number is halved. so sorry i said 46 but its actually 23 as the homologous chromosones have seperated.
Awesome thanks for explaining it to me!
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Waqar Y
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Mitosis = 46 chromosomes produced, two daughter nuclei from one parent cell.

Meiosis = 23 chromosomes produced, four haploid daughter nuclei produced(gametes, so 23 chromosomes from each parent = 46)

Other main differences, meiosis has two division stages, whilst mitosis just has one.
Meiosis has genetic variation, due to crossing over during Prophase, whilst mitosis is just a full copy.

Interphase is to replicate the chromosomes after they split at telophase in Mitosis.
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Elwyn
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Also try not to to refer to the number of chromosomes, by saying 46 or 23, as this is only specifc to humans. It is an easy trap to fall into as most exams questions I've seen aren't referring to humans. Use the terminology Diploid, Haploid, 2n and n. Also bear in mind chromosomes are not visible during interphase, they are unwound in the form of chromatin which you can't really see under a microscope.
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