As far as I know, a human somatic cell has the cell cycle:

Interphase and Replication (mitosis). In interphase, the cell has 2 growth phases (G1 + G2) and a synthesis one (S phase being in between G1 and G2). After G2 ends, the cell will start entering mitosis.

Until the S phase, the cell has only 23 chromosomes right? And only after the DNA has duplicated the number of chromosomes doubles (to 46).

Please correct me if I am wrong? And will the cell in the G0 phase (after duplication and before G1) have 23 or 46 chromosomes?

  • 1
    $\begingroup$ Is this question also considering chromosome aberrations like Trisomy 21? en.wikipedia.org/wiki/Trisomy#Human_trisomy Because that would break the question wouldn't it? $\endgroup$
    – Ro Siv
    Jan 16 '16 at 20:42
  • $\begingroup$ No, it refers to a general somatic cell division, assuming no chromosome aberrations. $\endgroup$
    – Vladimir
    Jan 16 '16 at 21:16
  • $\begingroup$ Most of the time DNA is not present as chromosome as such. $\endgroup$
    – JM97
    Mar 27 '17 at 15:22
  • $\begingroup$ It is also interesting to note that cancer cells often have more than 46 chromosomes due to mutations $\endgroup$
    – user35897
    Dec 8 '17 at 13:17

Humans have 46 chromosomes, 23 come from the mother and 23 come from the father. I think The easiest way to remember this is to think of the sex chromosomes--if you are male, you have one X chromosome from your mother and one Y chromosome from your father. During S-phase, the cell will make another copy of the X chromosome and the Y chromosome, so you will (technically) have 4 sex chromosomes in the cell before it divides, although you only have 2 UNIQUE sex chromosomes. After division, each daughter cell will have 2 sex chromosomes (one X and one Y). The same holds for all the other chromosomes.

So, to answer your question, yes, in G2 phase, you have double the amount of chromosomes in your cell (46*2 = 92), but you only have 46 UNIQUE chromosomes in your cell.

EDIT: As many people have pointed out, there are examples that do not conform to this rule. For example, both skeletal and liver cells can maintain a second copy of their chromosomes (making them 2n). This, however, is the exception. In my opinion, it's more valuable to know the basic rules that govern chromosomal number.

As an exercise I'd suggest to think about what it means that a cell has '2n' chromosomes? What happens if a germ cell obtains 2n chromosomes and passes that to a viable offspring? Is that offspring now '2n', or do they just have double the number of chromosomes as the parent? When does a duplicated chromosome become an it's own chromosome and not just a "duplicate copy"?

  • $\begingroup$ So let me see if I got this right. In interphase(till S-pase you have 46 chromosmes not 23) and after you duplicate the number you will have in G2 phase a bigger cell nucleus with 92 chromosmes not 46. And in mitosis each daughter cell will have 46 chroosmes. $\endgroup$
    – Vladimir
    Jan 16 '16 at 21:11
  • $\begingroup$ yes, minus some semantic issues, I think you have got it. I doubt you'll ever find someone agreeing that you "have 92 chromosomes". You merely have 2 copies of 46 unique chromosomes. BTW, if this answer is satisfactory, please accept my answer by clicking the checkmark next to my post $\endgroup$
    – lstbl
    Jan 16 '16 at 22:51
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    $\begingroup$ Liver cells can be polyploid... $\endgroup$
    – biogirl
    Jan 17 '16 at 2:16
  • $\begingroup$ Thank you @Istbl; but saying that you have two pairs of 46 chromosomes at one time is similar to having 96 chromosomes, still in interphase but after S-phase . @biogirl : Liver cells can have multiple chromosomes because they have more than one nuclei or in one of the nuclei they have more than 46 chromosomes ? $\endgroup$
    – Vladimir
    Jan 17 '16 at 8:07
  • $\begingroup$ As @biogirl said there are somatic cells in the body of a human that do not conform to the single nucleus, 2n genomic DNA. Skeletal muscle cells are polynuclear, so they have multiple nuclei with their own set of chromosomes. $\endgroup$
    – AMR
    Jan 17 '16 at 20:38

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