Question

difference between chromosome and chromatid

Answer 1

Though these terms are closely related and very confusing to each other, there are still a lot of things that differs each one of them. A long and continuous strand of DNA is what Chromosomes are but when two chromatids are united together with a centromere, it produces one chromosome. Chromosomes, as mentioned above, are vectors of heredity or the ones that carries the genes of one organism to the other like the physical appearance and different characteristics while Chromatids are the ones who made possible the replication of these cells.
These DNA terms are really confusing if not studied deeply due to the fact that they are interconnected with other. To put it in a picture wherein every one can understand, chromosomes when viewed in a microscope is like an X shape. Divide the X by half and it would result into > and <. A single > or < is what you call a chromatid. The center point of contact is the centromere and the whole X is the chromosome.

Answer 2

A chromosome consist of a DNA double helix bearing a linear sequence of genes.
During the cell division, more precisely during the S-phase of interphase, DNA is replicated. The resulting two identical copies of DNA are connected to each other at the centromere. Each copy is called a chromatid.