chromosome numbers

[wantVCUdental]

If an organism has a diploid number of 18, how many chromatids are visible at the end of mitotic prophase?

I thought it would be 72 chromatids, because if the diploid is 18, then in mitosis, it replicates DNA to 36 chromosomes by end of prophase and that means 72 chromatids...

answer is:

36...

could someone please elaborate? thanks

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[sw1sschez]

It is 36. Prophase just doubles whatever you have. You quadrupled it.

 

[azar87]

It is 36. Prophase just doubles whatever you have. You quadrupled it.

Think of this way diploid means two so as our diploid number is 2n each chromosome consists of two chromatids.....so if there are 18 chromosomes then we have 36 chromatides.

 

[failedmagician]

Hopefully this helps...

2n = diploid number..meaning that each chromatid now has a sister chromatid. So one chromosome = 2 chromatids.


Mitosis
Prophase thru Telophase =>2n = 18 chromosomes, 36 chromatids
Cytokinesis still 2n = 18 chromosomes, but now 18 chromatids

Meiosis:
Meiosis I Prophase: 2n=18 chromosomes, 36 chromatids (1 cell)
Meiosis II Prophase: n=9 chromosomes, 18 chromatids (2 different cells)
End of Meiosis II: n = 9 chromosomes, 9 chromatids (4 different cells)

 

[failedmagician]

If an organism has a diploid number of 18, how many chromatids are visible at the end of mitotic prophase?

I thought it would be 72 chromatids, because if the diploid is 18, then in mitosis, it replicates DNA to 36 chromosomes by end of prophase and that means 72 chromatids...

answer is:

36...

could someone please elaborate? thanks

If 2n=18 that does not mean 36 chromosomes. That means the cell has already made copies of DNA (S-phase) and now you have a diploid cell.

I think you are confusing 18 chromosomes (diploid) with 18 PAIRS of chromosomes==>36 individual chromosomes==>72 chromatids!

So for us (humans)...we are 2n = 46 or 23 pairs of chromosomes and 92 chromatids.
They normally talk about "pairs of chromosomes" when they are talking about tetrads during metaphase of meiosis I or bivalents.


haha I had a test on this not too long ago, that's why I'm elaborating so much 🙂

 

[wantVCUdental]

thank you guys very much,
so for humans, we have 46 chromosomes (23 pairs)
AFTER a round of replication (prior to mitosis) we have 46 pairs of chromosomes?
I wish i didn't sell campbell...