chromosomes

1. The small bodies in the nucleus of a cell that carry the chemical “instructions” for reproduction of the cell. They consist of strands of DNA wrapped in a double helix around a core of proteins. Each species of plant or animal has a characteristic number of chromosomes. For human beings, for example, it is forty-six.

In humans, sex is determined by two chromosomes: an X-chromosome, which is female, and a Y-chromosome, which is male. (See sex chromosomes.)