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 chromatids vs. DNA  



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Author4 Posts
  #1

does a chromosome generally contain of 1 strand of DNA or 2 strands of DNA?

on pictures of human chromosomes they always show 23 pairs of chromosomes, and each chromosome (at least, autosome) consists of 2 chormatids (and therefore looks like an X). we also know that during mitosis or meiosis each chromosome is indeed divided into 2 identical chromatids, which are tightly coiled DNA strands, and they drift apart to create new cells. my question is: in its normal state, not during mitosis/meiosis, does chromosome consist of 2 chromatids, or is it just a single DNA strand which only replicates immediately before division of the cell?

thank you very much!




  #2

double stranded


  #3

well you should note that what you refer to as " chromatides" are inface double-standed themselves; never single, b/c it is too unstable except in Viruses which is a diff. story.
having said that, each chromosome under norm. conditions, if is actively dividing, by the end of S phase (mitosis) contains two IDENTICAL chromatides attached at the Centromere which are EXACTELY the same. one a Replica of the other (through REPLICATION) and these identical chromatides during the next Metaphase dettach and form "Sister chromatides" which go to two new cells. and then the cycle repeats. but even when they are dettached and single they still are "DOUBLE-STRANDED".


  #4

yes, i realize that every chromosome/chromatid contains DNA which is in itself a double helix shaped molecule, or what you refer to as double-stranded. what i wonder about is whether there is 1 or 2 double helix shaped DNA molecules in a chromosome under normal conditions (not during the division of the cell)

the very fact that chromosomes, or actually DNA, replicate during mitosis/meiosis, doesn't it mean that before the division of the cell there was only one strand of the DNA molecule? and not every cell in the human body is undergoing division at any given moment

thank you!





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