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I know technically the question isn't really accurate but hopefully it gives the essence of what I'm trying to ask.

By the way I was taught in school, I was under the impression that a chromosome was made out of multiple complete copies of DNA. But, what I'm reading online makes it sound like a single complete string of DNA is broken up into sections and those sections are wound into chromosomes (so that one complete set of chromosomes would make up one complete string of DNA).

I'm assuming neither are 100% correct, but could someone explain it in a way that I can understand?

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    $\begingroup$ please cite what you are reading online $\endgroup$ – dblyons Jan 17 '17 at 1:14
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A chromosome is one long molecule of double-stranded DNA. As a diploid organism, you (almost certainly) have two copies of each autosomal chromosome; one from your father, one from your mother. You (almost certainly) inherited one copy of the X chromosome from your mother, and you either have a second one from your father, or you inherited a smaller Y chromosome instead.

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Is a set of chromosomes made up of many copies of DNA?

Yes, 23 different chromosomes (discrete ds DNA molecules) form a set of the pair in human beings.

Or is one complete string of DNA broken up into one set of chromosomes?

No. No such string of DNA with all the chromosomal materials fused together exist in any stage of a cell's life.

When a cell in not dividing it has 46 discrete ds DNA molecules.

Here's a karyotype of human male:

enter image description here

From: wellcomeimages.org

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Your second assumption is right. Dna is broken into various parts and then arranged into sets of chromosomes

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For this answer it might be useful to understand the different "stages" of genetic information.

The very root of genetic information is DNA. A section of DNA makes up a single gene. Genes are physically represented by loci (points) on a chromosome. What's more, chromosomes can fall into two categories: allosomes and autosomes. The former are what determines your gender, they contain all of the genetic data required to form the various proteins to eventually build your reproductive organs. The latter is everything else: your hair colour, eye colour, specific enzymes, etc are all made here.

This is useful to this question because it means that each chromosome contains sperate genes to control set functions. Thus, each chromosome is part of the same set of DNA - in the sense of the same genome (the complete genetic code in a given organism).

It would then be logical to arrive to the result that, in terms of your question, chromosomes are part of the same DNA "chain". One structure cut into chunks, if you will.

Hope that helps.

EDIT: My reference is: Genetics By, B. Guttman, A. Griffiths, D. Suzuki and T. Cullis.

EDIT: Please bear in mind that each chromosome is itself it's own module.

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  • $\begingroup$ Very interesting! I always assumed that DNA was one long strand. I didn't know that it doesn't exist as one entity, but rather is broken up into chromosomes. And I assume the entire DNA (I guess the correct term would be "genome"?) comprises all the chromosomes and the mitochondria (I think)? $\endgroup$ – thinkofacard Jan 17 '17 at 3:59
  • $\begingroup$ Good, I am glad! Yes genome would be the correct term. No. Whist chromosomes make up your genetic information, mitochondria are actually ancient bacteria that formed a biotymbiotic (both parties gain value from the following action) with a human cell, as ATP (energy) is formed by the mitochondria and the cell provides other necessities for the bacteria (mitochondria). So the mitochondria remains in the human. The bacteria has its own genome and is thus separate from our DNA. $\endgroup$ – rj60001 Jan 17 '17 at 7:39
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    $\begingroup$ -1: I'm sorry but this is just too inaccurate. To focus on the most glaring mistake, chromosomes are most certainly not part of the same DNA chain! Each of them is a distinct molecule. $\endgroup$ – terdon Jan 17 '17 at 10:44
  • $\begingroup$ That is correct, in the sense that they are completely separate from one another as distinct entities, but they are still ultimately part of the same genome, of which I think is a suitable answer the question he is asking. They are certainly not copies of the same DNA if that is the answer you are supporting. $\endgroup$ – rj60001 Jan 17 '17 at 11:10
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    $\begingroup$ I completely agree with @terdon. Chromosomes are not part of the same "DNA chain". You are implying that eukaryotic multi-chromosomal DNA somehow has a "natural state" where you can connect all the chromosomes together, if you wish. A genome is not a "chain" - it is composed of individual, separate elements (chromosomes), which exist independently - you cannot just splice them together and expect them to work in the same way. Telomeres are one reason, the issue of multiple centromeres and what happens during mitosis (independent assortment) is another. $\endgroup$ – MattDMo Jan 17 '17 at 18:53

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