A chromosome is one long, tightly coiled molecule. Which substance is that molecule?

Explanation

A chromosome is a single very long molecule of deoxyribonucleic acid, packed tightly so that it fits inside a cell, and the genes along it are named stretches of that same molecule. Saying it is made of genes alone leaves out the material those genes are written in, a gene is far shorter than the whole chromosome carrying it, and treating the coiled molecule as protein puts the genetic material somewhere it is not.