Does a chromosome have one or two chromotids?

Question

I am getting confused about the interphase stage in cell cycle. I read that chromosome is a single double helix of dna, which is like 1 chromatid, right? ..but then , I read that a chromosome have 2 chromatids..so which one is it? 1 or 2? Is it still called chromosome with just 1 chromatid? Am I missing something here? I just don't get this interphase stuff. I understand what is happening in the other stages, but I am not clear about the chromosome part in interphase. Sorry, I am a math major, but taking this class for the science requirement. If you can, please help. Thank you

Thanks to all that have posted. But I still don't get it. Please just stick to the interphase stage, does the chromosome have 1 or 2 chromatids? Just Gap1 to Gap2. That's all I need. Thanks!

Answer 1

During early interphase when the DNA has not doubled, the DNA is in the form of chromatin ... thin, shapeless masses. In later interphase, after the S phase, DNA has been doubled, but it still hasn't formed into chromosomes. That happens during prophase. When the chromatin condenses to form chromosomes, the DNA has been copied, so the chromosomes have two chromatids, each chromatid having one copy of the DNA for that chromosome.

Additional:
In G1 the DNA is single. It's in the form of chromatin, but there is only one strand.

In S the DNA replicates and becomes double stranded.

In G2 the DNA is already copied and is double-stranded. However, it still LOOKS the same because it's in the form of chromatin. No chromosomes are apparent at any stage of interphase.

Answer 2

one chromosome has 2 sister chromatids which are identical. when the cell is not replicating, the chromosome has one chromatid. then, during replication it makes another identical one, and thus has 2 chromatids (the X looking thing). then they separate during cell division and each daughter cell has 1 chromatid. hope that made sense :p