What Is a Chromosome?
By Brandon Colby, MD, Physician specializing in genetic analysis and personalized preventive medicine, and author of Outsmart Your Genes.
A chromosome is a tightly coiled structure made of DNA and proteins, located in the nucleus of a cell. Chromosomes package long strands of DNA so they fit efficiently inside cells and can be accurately copied and divided when cells reproduce.
Humans typically have 23 pairs of chromosomes (46 total) in each cell: 22 pairs of “autosomes” and one pair of sex chromosomes (XX or XY). One chromosome in each pair comes from the mother and one from the father. Changes in chromosome number or structure — such as an extra copy of chromosome 21, which causes Down syndrome — can have significant effects on development and health.
References: medlineplus.gov/genetics; genome.gov