One of the pair of chromosomes determining sex; in humans designated an X chromosome and a Y chromosome, with females having an XX genotype and males an XY genotype.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 804 (https://doi.org/10.1515/pac-2015-1202)