why does each chromosome have a chromatoid?

Answer 1

A chromatid is one of two identical strands of DNA making up a chromosome that are joined at their centromeres, for the process of nuclear division (mitosis or meiosis). The term is used so long as the centromeres remain in contact. When they separate (during anaphase of mitosis and anaphase 2 of meiosis), the strands are called daughter-chromosomes.The tips of the chromatid are called telomeres.They are there to prevent the ends of the chromosome from attaching to other chromosomes. It has been said that after repeated cell replication, the telomeres gets shorter resulting in cell death. Thus, this mean that the way telomeres work could play a role in determine the lifespan of a cell.However this has not been proven.[1]

In other words, a chromatid is "one-half of a replicated chromosome".[2] It should not be confused with the ploidity of an organism, which is the number of homologous versions of a chromosome.

Answer 2

We only see chromosomes during mitosis or meiosis. The rest of the time the DNA is in the form of chromatin. So when we see a chromosome, the DNA has been duplicated in preparation for cell division. The chromosomes are double-stranded with the two sister chromatids being identical. They stay double-stranded until the centromeres are pulled to opposite poles during anaphase of mitosis or during anaphase II of meiosis.