A chromosome unit is a single GENE, which is a segment of DNA that contains the instructions for making proteins. Genes are made up of four nucleotide bases: adenine, thymine, guanine, and cytosine. Chromosomes are made up of many genes, and each GENE has a specific function in the body. Chromosome units are essential for the proper functioning of the body, as they provide the instructions for making proteins that are necessary for life.