Diagram of a duplicated and condensed metaphase eukaryotic chromosome.
(1) Chromatid – one of the two parts of the chromosome after duplication.
(2) Centromere – the point where the two chromatids touch.
(3) Short arm. (4) Long arm.

Chromosomes of nonbiting midge larvae, prepared and stained

Drosphila melanogaster polytene chromosomes. This shows chromosome activity after a heat shock

The chromosomes of a cell are in the cell nucleus. They carry the genetic information. Chromosomes are made up of DNA and protein combined as chromatin. Each chromosome contains many genes. Chromosomes come in pairs: one set from the mother; the other set from the father. Cytologists label chromosomes with numbers.