Chromosome, Chromatin and Chromatids – What is the Difference?
Chromosome, chromatin and chromatids – these terms sound very similar and that is why it can be confusing sometimes. So let’s start from chromatin and then will move to chromosome and then to chromatid. Why this particular order? You will know once you read it. It becomes very easy to understand in this order.
DNA is our genetic material and it is too long (about 2m) to be fit inside the small nucleus (5μm – 10μm in diameter). So in order to fit inside the nucleus, DNA has a packaging strategy. And this strategy involves wrapping of DNA around the histone proteins. So our double stranded DNA would wrap around histone proteins. This assembly where we have DNA and histone (DNA + Histone) looks like thread is called CHROMATIN. And this DNA in chromatin phase is not condensed yet.
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Chromatin = DNA Wrap around Histone Proteins OR DNA + Histone Proteins
Now when cell undergoes cell division, the DNA will start getting condensed (remember in chromatin phase as we just saw DNA is not condensed). So this condensed form of DNA is called CHROMOSOME.
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Chromosome = Condensed form of DNA
When the cell is dividing, each chromosome needs to replicate and make its identical copy. To achieve this each chromosome duplicates itself and they will be attached at the point of centromere. This assembly where we are observing DUPLICATED chromosome initially attached at the point of centromere, each strand in that or copy in that is called CHROMATID. We sometimes refer to it as sister chromatids when we talk about recombination right!! So the chromatid is nothing but duplicated chromosome which has not yet separated. Now when cell will divide each of the new cell will get one copy of chromatid and this chromatid will act as chromosome itself in that new cell. (The same chromatid would decondenses into a chromatin strand)
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Chromatids = Duplicated Chromosome Attached at the Point of Centromere
Read complete short note on this topic here.
Read in depth on chromatin from an online book.