Number of DNA molecules in a chromosome

[fmjones2]

In a chromosome (i.e. 2 chromatids), is it correct that there are 2 separate (and identical) molecules of DNA? On Wikipedia, the definition of chromosome is stated as "a single piece of coiled DNA" (http://en.wikipedia.org/wiki/Chromosome), but I believe they mean a single chromatid is a single piece of coild DNA, correct?

[han.allanchan]

One chromosome is made up of one single double-stranded DNA which is wrapped around the proteins, histones which is highly positively charged. If you are talking about a pair of chromosomes, it should be two chromatids with 2 identical double stranded DNAs which are held together in antiparallel orientation by H-bonds. Hope it helps.

Edited December 9, 2013 by han.allanchan

[CharonY]

It depends on organism and growth phase. For eukaryotes the most precise assertion is that chromatids contain a single DNA molecule. The definition are slightly loose, due to historic reasons I presume. Prior to the S-phase the chromsome has only one DNA molecule, but after replication it consists of two chromatids. What may be confusing is that most of the time chromatids is only referred to the sister chromosomes after duplication, but when they separate they are often not referred to as chromatids anymore, but as chromosomes.