Chromatin, Chromosome and Chromatid
Many times biologists represent a DNA molecule with a simple thread diagram.
This simple thread diagram abstracts all those base pairs rungs as well as two sides of DNA composed of sugar and phosphate groups.
Chromatin:
- When a DNA molecule is wrapped around proteins called histones then we get chromatin.
- These histones give structure to the molecule.
- Chromatin is loosely packed and dispersed within the nucleus.
- For an analogy you can think of chromatin as noodles spreaded loosely in a bowl. You can assume the bowl as the nucleus.
Chromosome is the condensed version of chromatin.
Most of the time in a cell’s life cycle we have the chromatin version and not the chromosome. Chromosome version is acquired during the cell division. Now, the question is: why does it condense and take the chromosome form? Answer is: it is easy to separate the copied genetic material when we have condensed structures. Chromosomes ensure accurate DNA segregation during cell division. Let me give an analogy to make this point clear. You can assume this chromatin as an unwound woolen ball. Yes, the one with which a sweater is knitted. The tightly wounded woolen ball can be assumed as a chromosome. Now, in one case if I give you a mess of unwounded woolen threads and in another case I give you perfectly wounded woolen balls then in which case will it be easier for you to separate them? I hope you got the answer.
Mistakes during copying, or unequal division of the genetic material between cells, can lead to cells that are unhealthy or dysfunctional (and may lead to diseases such as cancer).
Chromatid:
Now most of the time you must have seen that x-like diagram of chromosomes. This is the case when genetic material is duplicated and the chromosome is ready to split into two individual chromosomes. So at this stage these two copies within a single chromosome which are not yet separated are called chromatids. Once they are separated they are called as two new individual chromosomes. So, one matured chromosome having sister chromatids in it goes through the division process which results in two individual chromosomes.
Reference:
- Khan Academy
