How are the concepts of chromosomes, chromatin and chromatids related? During which phase of the cell cycle does DNA replicate?

Answer 1

Chromatin-- is all of the genetic material in your cells. It is DNA when it is "unwound". Essentially, it is not in tight little bundles like chromsomes. The entire point of having chromatin is so DNA can replication.

THIS REPLICATION HAPPENS IN INTERPHASE, MORE SPECIFICALLY, S PHASE OF INTERPHASE.

Chromosomes-- are the little units that your DNA is made out of. Essentially, they are little bundles of genes that go together. They can have 2 copies of each gene (the two copies are each a chromatid) after DNA has replicated or, just one copy of the DNA if, it has not replicated.

Chromatids-- are the parts of the chromosome that spilt apart. When a chromosome has 2 copies of the same DNA, each chromatid is one copy.

Think of it this way, I am making a photocopy of a big packet to give to my friend.

When I take it all apart, everything is still there- but its a little bit of a mess! Its all opened up like this so I can copy it... it won't fit in the photocopier stabled together. That, is Chromatin, the purpose of unwinding DNA to make chromatin is so that it can be copied.

Then, I have two identical packets. Imagine that I hold each one together with a staple and then, hold both stapled packets together with a paperclip. I have to staple them and paperclip them so I don't misplace either one, or mix up a page of one with the pages of the other-- that is why DNA coils into chromosomes before it divides.

Each stabled packet is a chromatid. The paper-clipped unit is a chromosome. Both chromosomes and chromatids have all of the genetic material in an organized manner. Chromatids are part of the chromosome!

Now, this is the only part that is a little confusing. Once the packets are split, and my friend has his own, each one is a chromosome on its own! Because it has all of the material.

Think of it this way. When both are paper-clipped together, they are parts of one big indistinguishable packet. Until I take one out of my back pack, and give one to my friend, then each is a complete packet! Each one can go into its own "cell" for example, if I put mine into my backpack and my friend puts his into his backpack.