020200
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Hi,

I know that 1 human diploid cell has 23 pairs of chromosomes. Does each chromosome in each pair have 2 chromatids?

Thanks.
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Jpw1097
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(Original post by 020200)
Hi,

I know that 1 human diploid cell has 23 pairs of chromosomes. Does each chromosome in each pair have 2 chromatids?

Thanks.
It depends on which stage of the cell cycle you're talking about. Most cells spend their time during interphase (or may be quiescent), in which case the DNA is in a loose form known as chromatin. In chromatin, there are no discrete structures or chromosomes like there are during mitosis, and the DNA is not replicated most of the time. During S phase of interphase, the DNA (still as loose chromatin) replicates. During prophase (first phase of mitosis), the DNA condenses to form chromosomes which, since the DNA has already been replicated, consist of two chromatids joined at the centromere. During anaphase of mitosis, the chromatids are pulled to opposite poles of the cell. During telophase (the final phase of mitosis), the DNA decondenses back into the loose chromatin. So chromosomes are only present from prophase to telophase (mitosis), and each chromosome consists of chromatids from prophase to anaphase, when they are separated.
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username2858058
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yes
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020200
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(Original post by Jpw1097)
It depends on which stage of the cell cycle you're talking about. Most cells spend their time during interphase (or may be quiescent), in which case the DNA is in a loose form known as chromatin. In chromatin, there are no discrete structures or chromosomes like there are during mitosis, and the DNA is not replicated most of the time. During S phase of interphase, the DNA (still as loose chromatin) replicates. During prophase (first phase of mitosis), the DNA condenses to form chromosomes which, since the DNA has already been replicated, consist of two chromatids joined at the centromere. During anaphase of mitosis, the chromatids are pulled to opposite poles of the cell. During telophase (the final phase of mitosis), the DNA decondenses back into the loose chromatin. So chromosomes are only present from prophase to telophase (mitosis), and each chromosome consists of chromatids from prophase to anaphase, when they are separated.
Thanks for the explanation! So would that mean that a normal cells not yet undergoing cell division consists of 23 chromosomes - each of these chromosomes consists of JUST 1 chromatid?

Thanks!
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(Original post by 020200)
Thanks for the explanation! So would that mean that a normal cells not yet undergoing cell division consists of 23 chromosomes - each of these chromosomes consists of JUST 1 chromatid?

Thanks!
Kind of, although it would be wrong to call them chromosomes because chromosomes refers to the DNA when it is tightly packed. Most of the time, DNA is loose and no chromosomes are visible - we call it chromatin instead. But yes, most of the time, there is only one copy of the DNA (i.e. it is not replicated).
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