Cell cycle question!

[virtualmaster999]

Hi everyone!

I came across something I got a little confused about.

In mitosis, say you start with 46 chromosomes (2N). At anaphase you will have 46 of the 92 chromatids going to one side, and the other 46 going to the other side (considered chromosomes at this point) So going from 46 (2N) to 92 in (4N). Does this 4N continue for telophase, since the cell hasn't split yet, or are they considered separate cells in telophase? I'm guessing this situation also applies to meiosis 1/2.

Any feedback helps. Thank you in advance!!

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[cacajuate]

It continues into telophase until cytokinesis happens in mitosis and meiosis 1. But why doesn't it happen in meiosis 2? That is a big point and you should look into that and see why that is the case.


But when they are referring to 4n amount of 92, that is the amount of chromatids not chromosomes. You never end up with more than 46 chromosomes in a cell.


I sure hope I got that all right...

 

[w4nt2baDDS]

You never end up with more than 46 chromosomes in a cell.

By technicality, once the sister chromatids are pulled apart they are considered individual chromosomes. Thus at the end of anaphase and the beginning of telophase a somatic human cell will indeed have 92 chromosomes present.

Meiosis 2 is more similar to mitosis than meiosis 1.

 

[cacajuate]

hmmm...I guess I don't know it as well as I thought but I still don't think there are ever 92 chromosomes present. 92 chromatids yes, but never more than 46 chromosomes.

...looks like I really need to read up on this again.

paging @FeralisExtremum to help clarify.

 

[FeralisExtremum]

w4nt2baDDS has it right, when the chromatids are pulled apart they are considered individual chromosomes. So during Anaphase (and Telophase until the cells are completely separated) of mitosis, we have 92 chromosomes. Once the cells fully separate, the normal total count of chromosomes in a somatic cell is restored (46).

During meiosis you will never have 92 chromosomes, but up until the completion of Telophase I you will have 92 chromatids.

Here is a table that recaps all of this:

 

[virtualmaster999]

w4nt2baDDS has it right, when the chromatids are pulled apart they are considered individual chromosomes. So during Anaphase (and Telophase until the cells are completely separated) of mitosis, we have 92 chromosomes. Once the cells fully separate, the normal total count of chromosomes in a somatic cell is restored (46).

During meiosis you will never have 92 chromosomes, but up until the completion of Telophase I you will have 92 chromatids.

Here is a table that recaps all of this:

You're a lifesaver Feralis!

 

[tooth_hurty]

I think the part where it can get tricky is at anaphase of mitosis vs meiosis I. But since we know that meiosis I produces 2 haploid cells through reductional division (UNLIKE mitosis), it makes sense that each cell has 23 chromosomes and 46 chromatids because we're splitting whole chromosomes, not chromatids. So everything is halved after cytokinesis and the 2 cells are now haploid.

And then in meiosis II, we have equational division which is IDENTICAL to mitosis - but we start with half the number of chromosomes and chromatids. Chromatids split, each now considered a whole chromosome, and after cytokinesis we get 4 haploid gametes.

*Just felt like typing this out so I can remember it lol. Thank you @FeralisExtremum that table is gold

 

[tbogdan89]

And on top of Feralis' amazing chart, I also use this to apply it to any chromosome #. I found this from an older thread and memorized it, the thread should still be around somewhere
Mitosis:
# Chromosomes / # Chromatids
Prophase: 2N / 4N
Metaphase: 2N / 4N
Anaphase: 4N / 4N
Telophase: 4N / 4N
Cytokinesis: 2N / 2N

Meiosis I:
# Chromosomes / # Chromatids / # Tetrads
Prophase: 2N / 4N / N - *Crossing over / Synapsis occurs
Metaphase: 2N / 4N/ N -
Anaphase: 2N / 4N - Separation of Homologous chromosomes; *Non-Disjunction possible
Telophase: 2N / 4N
Cytokinesis: N / 2N

Meiosis II:
# Chromosomes / # Chromatids
Prophase: N / 2N
Metaphase: N / 2N -
Anaphase: 2N / 2N - Separation of Sister chromatids; *Non-Disjunction possible
Telphase: 2N / 2N
Telophase: N / N

 

[510586]

Cytokinesis begins at telophase right? Seems like no one has a definite answer to this.

 

[FeralisExtremum]

Cytokinesis begins at telophase right? Seems like no one has a definite answer to this.

Can vary with species but for humans it happens around the end of Anaphase

 

[510586]

Thanks