cell cycle

[deleted738762]

Mitosis you start off with 46 chromosomes or 92 tids. Then you produce 2 cells and get 46 chromosomes and 46 tids. How do you get the same # of chromosomes and tids?

Then Meiosis 1 you have 46 chromosomes and 92 tids. So 23 homologous pairs and 46 tids get produced. Makes sense because 2 cells.

Then in Meiosis 2 you have 46 chromosomes and 92 tids. Then you produce 23 chromosomes and 23 tids? How do you go from 92 tids to 23 tids? It makes 0 sense because the number should be similar to mitosis since your still only making 2 cells here.

Can someone clear it up. This is so annoying!
Thanks

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[deleted738762]

 

[Mrhyde]

"Mitosis you start off with 46 chromosomes or 92 tids. Then you produce 2 cells and get 46 chromosomes and 46 tids. How do you get the same # of chromosomes and tids?"

lol why not just type the full word "Chromatid" ... Anyways this is a good question that I was confused at first about also. The answer is, that we Count a Chromosome as a Chromosome by counting the number of Centromeres .... When we first start off we have 46 chromosomes so 46 Centromeres ... then when we split into 2 cells, well the Centromeres also split so we are still at 46 chromosomes. When we reach the S phase at interphase we will add a Chromatid so are chromosome goes from looking like this: / to X BUT we did not add Centromeres so we are still at 46

"then in Meiosis 2 you have 46 chromosomes and 92 tids. Then you produce 23 chromosomes and 23 tids? How do you go from 92 tids to 23 tids? It makes 0 sense because the number should be similar to mitosis since your still only making 2 cells here."


Notice: that the HUGE difference between Mitosis and Meiosis I , is that during Prophase I, we have the Homologs "pair" (Synapsis), which is what ultimately causes the cells to end up haploid, Since during Anaphase I we have the tetrad pair, de-paired which allows us to end up Haploid with an even split of 23 and 23.

While during Mitosis we don't have a pairing , which means that during regular Anaphase, one Chromosome gets pulled into 2 chromatids which ends up giving us Diploid cells. 46 and 46 since we count chromosomes by Centromeres.

 

[deleted738762]

"Mitosis you start off with 46 chromosomes or 92 tids. Then you produce 2 cells and get 46 chromosomes and 46 tids. How do you get the same # of chromosomes and tids?"

lol why not just type the full word "Chromatid" ... Anyways this is a good question that I was confused at first about also. The answer is, that we Count a Chromosome as a Chromosome by counting the number of Centromeres .... When we first start off we have 46 chromosomes so 46 Centromeres ... then when we split into 2 cells, well the Centromeres also split so we are still at 46 chromosomes. When we reach the S phase at interphase we will add a Chromatid so are chromosome goes from looking like this: / to X BUT we did not add Centromeres so we are still at 46

"then in Meiosis 2 you have 46 chromosomes and 92 tids. Then you produce 23 chromosomes and 23 tids? How do you go from 92 tids to 23 tids? It makes 0 sense because the number should be similar to mitosis since your still only making 2 cells here."


Notice: that the HUGE difference between Mitosis and Meiosis I , is that during Prophase I, we have the Homologs "pair" (Synapsis), which is what ultimately causes the cells to end up haploid, Since during Anaphase I we have the tetrad pair, de-paired which allows us to end up Haploid with an even split of 23 and 23.

While during Mitosis we don't have a pairing , which means that during regular Anaphase, one Chromosome gets pulled into 2 chromatids which ends up giving us Diploid cells. 46 and 46 since we count chromosomes by Centromeres.

Ok. If you have 46 chromosomes or 46 centromeres, then you split up into two separate cells, then each should have 23 chromosomes or 23 centromeres in each cell right?

 

[Mrhyde]

Ok. If you have 46 chromosomes or 46 centromeres, then you split up into two separate cells, then each should have 23 chromosomes or 23 centromeres in each cell right?

Exactly if we are talking about Mitosis then this splitting would happen in Anaphase.
But at the end of Telaphase each chromosome in the two cells we just made that has 46 chromosomes in cell1 and 46 in cell2 - is made of only one chromatid ...SO... we make the 2nd chromatid during interphases S phase , but at the end of interphase we still have 46 chromosomes because even though we added a chromatid during the S phase, it just added to the same centromere of each chromosome. (So we did not add centromeres )

 

[deleted738762]

Exactly if we are talking about Mitosis then this splitting would happen in Anaphase.
But at the end of Telaphase each chromosome in the two cells we just made that has 46 chromosomes in cell1 and 46 in cell2 - is made of only one chromatid ...SO... we make the 2nd chromatid during interphases S phase , but at the end of interphase we still have 46 chromosomes because even though we added a chromatid during the S phase, it just added to the same centromere of each chromosome. (So we did not add centromeres )

So a centromeres connects two chromatids. So you have 46 centromeres Then they get divided because they get put into two daughter cells. So you would have 23 centromeres in a daughter cell. So at the end of mitosis you only have 23 centromeres in each daughter cell, not 46!. The only way it gets to 46 is during interphase like you said, but interphase happens after mitosis so how can they say mitosis is separate from interphase, but then use interphase to justify the number 46. Do you see where I am coming from?

 

[Mrhyde]

So a centromeres connects two chromatids. So you have 46 centromeres Then they get divided because they get put into two daughter cells. So you would have 23 centromeres in a daughter cell. So at the end of mitosis you only have 23 centromeres in each daughter cell, not 46!. The only way it gets to 46 is during interphase like you said, but interphase happens after mitosis so how can they say mitosis is separate from interphase, but then use interphase to justify the number 46. Do you see where I am coming from?

I think you are confusing yourself because when you talk about Mitosis and Meiosis it would be easier to understand if you ask your questions relating to specific phases of the process. You need to understand that the cell cycle is a continuous process , so before Mitosis and at some point after Mitosis we have interphase since this will have to go full circle if its a repeating continuous process . Interphase is when we get the 2nd chromatid. So in your example that you said it would go like this:

So a centromere connects two chromatids. and two chromatids connected in the middle by one centromere is considered one chromosome . One chromatid not connected to another chromatid can exist and this one chromatid not connected to anything would still be considered one chromosome since it has 1 centromere . But once it reaches interphase it will get another chromatid copy but it would still be considered one chromosome since it has 1 centromere even though it just went for "/" to "X".

let me give you an example with one chromosome....

When we start Mitosis , it would be after interphase so the chromosome will look like "X". then when "X" splits in Anaphase we would now have one "/" in one cell and one "/" in the other. But you can think of it like as if each chromosome retained a small piece of the centromere when they split so think of the centromere in each "/" healing which will now give us 2 centromeres. Lol


During Anaphase, the microtubules that are attached to the kinetochores contract, which pulls the sister chromatids apart and toward opposite poles of the cell. At this point, each chromatid is considered a separate chromosome.

 

[TrueMenace]

The key to understanding this is this simple idea:

1 chromatid = 1 chromosome.

A homologous chromosome has 2 chromatids joined at the centromere. When they separate, it becomes 2 chromatids which are 2 chromosomes.

 

[deleted738762]

"So you have 46 centromeres Then they get divided because they get put into two daughter cells. So you would have 23 centromeres in a daughter cell. "

I think you are confusing yourself because when you talk about Mitosis and Meiosis it would be easier to understand if you ask your questions relating to specific phases of the process. You need to understand that the cell cycle is a continuous process , so before Mitosis and at some point after Mitosis we have interphase since this will have to go full circle if its a repeating continuous process . Interphase is when we get the 2nd chromatid. So in your example that you said it would go like this:

So a centromere connects two chromatids. and two chromatids connected in the middle by one centromere is considered one chromosome .
let me give you an example with one chromosome....
When we start Mitosis , it would be after interphase so the chromosome will look like "X". then when "X" splits in Anaphase we would now have one "/" in one cell and one "/" in the other. But you can think of it like as if each chromosome retained a small piece of the centromere when they split so think of the centromere in each "/" healing which will now give us 2 centromeres. Lol




During Anaphase, the microtubules that are attached to the kinetochores contract, which pulls the sister chromatids apart and toward opposite poles of the cell. At this point, each chromatid is considered a separate chromosome.

Ahh so even though X has one centromere, / also has one centromere. So if I have / in one cell and / in another cell they both have their own centromere now? So basically / retains a centromere, making the tid a chromosome because it has one centromere?

 

[deleted738762]

The key to understanding this is this simple idea:

1 chromatid = 1 chromosome.

A homologous chromosome has 2 chromatids joined at the centromere. When they separate, it becomes 2 chromatids which are 2 chromosomes.

I thought a chromosome has two sister tids. Homologous chromosomes have 4 tids. WTH?

 

[Mrhyde]

Ahh so even though X has one centromere, / also has one centromere. So if I have / in one cell and / in another cell they both have their own centromere now? So basically / retains a centromere, making the tid a chromosome because it has one centromere?

Yep that's the way I look at it

 

[Mrhyde]

Re read my post I just added this

So a centromere connects two chromatids. and two chromatids connected in the middle by one centromere is considered one chromosome . One chromatid not connected to another chromatid can exist and this one chromatid not connected to anything would still be considered one chromosome since it has 1 centromere . But once it reaches interphase it will get another chromatid copy but it would still be considered one chromosome since it has 1 centromere even though it just went for "/" to "X".

 

[TrueMenace]

I thought a chromosome has two sister tids. Homologous chromosomes have 4 tids. WTH?

Sorry my bad. Yea, a pair of homolougos chromosomes has 4 chromatids. One of those pairs has 2 sister chromatids, that when separated, become a chromosome. Hardest thing with this is the terminology.

 

[deleted738762]

Yep that's the way I look at it

Makes sense thanks.

 

[deleted738762]

Re read my post I just added this

So a centromere connects two chromatids. and two chromatids connected in the middle by one centromere is considered one chromosome . One chromatid not connected to another chromatid can exist and this one chromatid not connected to anything would still be considered one chromosome since it has 1 centromere . But once it reaches interphase it will get another chromatid copy but it would still be considered one chromosome since it has 1 centromere even though it just went for "/" to "X".

Yea I derived that as well from what you said before. Thanks again.

 

[deleted738762]

Yea I derived that as well from what you said before. Thanks again.

So I used that logic and this worked out well. Peep the file.. @Mrhyde

 

[super frank]

http://datbootcamp.com/biology-strategy/chromosome-and-chromatid-numbers-during-mitosis-and-meiosis/

 

[Mrhyde]

So I used that logic and this worked out well. Peep the file.. @Mrhyde

Umm You need to have a chart that's more detailed with PHASES listed not just the general term of Mitosis or the general term Meiosis you need Meiosis 1 and the phases and then Meiosis 2 and the phases all broken down etc. to really study it to understand it .......... , For example a common trick question is , During Anaphase of Mitosis how many Chromatids and Chromosomes are there? The answer would be 92 chromatids And 92 Chromosomes . This link breaks down the number count for you :
http://www.biologyexams4u.com/2013/04/chromosome-and-chromatid-count-in.html

 

[deleted738762]

Damn I am a geni

Umm You need to have a chart that's more detailed with PHASES listed not just the general term of Mitosis or the general term Meiosis you need Meiosis 1 and the phases and then Meiosis 2 and the phases all broken down etc. to really study it to understand it .......... , For example a common trick question is , During Anaphase of Mitosis how many Chromatids and Chromosomes are there? The answer would be 92 chromatids And 92 Chromosomes . This link breaks down the number count for you :
http://www.biologyexams4u.com/2013/04/chromosome-and-chromatid-count-in.html

If u sent me the picture or the link before I would have been able to visualize the centromere concept much more easily.

 

[Mrhyde]

Damn I am a geni

If u sent me the picture or the link before I would have been able to visualize the centromere concept much more easily.

Lmao, I guess typing answers helps me remember and study also

 

[DentalNucleicAcid]

I thought a chromosome has two sister tids. Homologous chromosomes have 4 tids. WTH?

I understand your frustration with this, I've been there. We've been lied to in school when they told us that "this is what a chromosome looks like" while they point to a replicated chromosome that's in the shape of an "X". That's NOT what a regular chromosome looks like, that's a replicated chromosome, i.e. it's ready start mitosis. A chromosome that has not undergone S phase looks like a single strand, i.e. 1 chromatid. So a regular, everyday chromosome looks like a single strand (that is, after it condenses). That's what they never told us in school and that's why I was confused on this very topic beginning from AP bio up until my DAT studies. However, a replicated chromosome with 2 chromatids and a chromosome that has not been replicated and only has 1 chromatid are both referred to as a single chromosome (because each of them have 1 centromere).