A normal human cell is diploid that contains 46 chromosomes in 23 pairs. Thus, when the cell undergoes mitosis, the cells still has the full chromosome with the two sister chromatids. What is it doing in interphase when it produces the other chromosomes?

I thought that the sister chromatids were pulled apart and, in interphase, the single sister chromatid grew another one. How is this possible if a human diploid cell contains 23 pairs of 2 chromosomes each?

  • $\begingroup$ No division takes place in interphase. $\endgroup$ – Anubhav Goel Mar 21 '16 at 11:33

The terminology of "chromosome" during this process is confusing, but here it is:

  • There are 46 chromosomes in the cell (23 pairs)
  • Before division, each chromosome has two sister chromatids, joined in the middle (92 chromatids in total)
  • During division, the chromosomes split and each daughter cell gets 46 chromatids, one from each chromosome
  • These chromatids are now known as chromosomes
  • Each one of these new chromosomes only has one "chromatid"
  • During interphase, the new chromosomes replicate and now they have two chromatids each, joined in the middle

So whether a chromosome has one or two chromatids it is still called a chromosome. I hope this helps.

The following link contains a more complete explanation of mitosis. The first picture explains this point quite succintly: http://biology.tutorvista.com/cell/mitosis.html

  • $\begingroup$ Joe-can you add some references to your answer... it will strengthen the answer and allow other individuals to read more about the question/answer. I know it may seem silly when questions have a very easy answer that is based on common knowledge of those in the field, but we do have users as young as high school students (and potentially younger) that benefit from cited references. Thanks for your contribution! $\endgroup$ – Vance L Albaugh Jan 16 '17 at 16:35
  • $\begingroup$ Thanks for the advice, I've added a link to a more complete explanation with figures. $\endgroup$ – Joe Boyle Jan 16 '17 at 18:07

In a diploid cell the two sets of chromosomes are called homologous chromosomes (except in the case of XY pair) and not sister chromatids. Sister chromatids refer to the exact duplicate daughter chromosomes produced after DNA replication during mitosis.

After mitosis each cell receives a copy of all the pairs of homologous chromosomes.

I hope your doubt is clear now.


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