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chromatids in mitosis & meiosis - quick que (Oct/22/2008 )

The last question of an assignment I have is making me go crazy so if someone has time to see if my answers are correct it would be much appreciated :]

A normal diploid human cell has 23 pairs of chromosomes. It also has 23 pairs of chromatids, & usually 1 chromosome consists of 1 chromatid. After DNA synthesis, the cell now has 92 chromatids (23 pairs = 26 x 2 = 92). Those chromatids are stuck together, so there are still 23 pairs of "chromosomes", each chromosome now consisting of 2 chromatids.

a) How many CHROMATIDS will that cell have in metaphase of mitosis ? I guessed 46, but that can`t be right...

cool.gif How many chromatids will one daughter cell have after mitosis is complete ? I thought 23 ?

c) How many would one daughter have in METAPHASE II of meiosis ? I thought 46 ?

d) How about after meiosis is complete ? I thought 23 ?


This is a badly worded question - chromatids only form during S phase and are present through to M, they are not present in G1

the cell now has 92 chromatids (23 pairs = 26 x 2 = 92)

I presume you made a typo and mean 46 not 26.

1) the answer is in the preamble to the question
2) At the completion of mitosis, the sister chromatids have been separated and formed daughter chromosomes, which are technically not chromatids.
3) Metaphase II is where the sister chromatids are paired, but not yet separated -there are 23 chromosomes from meiosis I but they are still in chromatid form I think, it has been a long time (15 years or so) since I have done any of this.
4) yes, looks right, though I think they would be called chromosomes at this point.

The distinction between haploid and diploid is the number of centromeres present, if that helps.


how did 23 become 26?
i'm no math genius, but usually 26 x 2 is 52.... laugh.gif

have a nice friday! yeah! biggrin.gif