A chromosome is a part of the nucleus of a cell, made up of a very long strand of DNA containing numerous genes (hundreds to thousands). A human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes. The 23rd pair is the pair of sex chromosomes (X and Y) that determines the sex of the foetus. Male bodies have one X and one Y chromosome, and female bodies have two X chromosomes. There are a number of variations of sex chromosomes beyond the XX/XY binary model, such as X0 or other.
