Sex chromosomes. Computer artwork of the human X (lower right) and Y (lower left) sex chromosomes. Other chromosomes are seen in the background. Each chromosome has replicated to form an identical copy, or chromatid, to which it is joined. The combination of sex chromosomes inherited during fertilisation, determines a person's sex. Males inherit an X and a Y chromosome. Females inherit two copies of the X chromosome. The Y chromosome contains instructions for the development of male characteristics. The sex chromosomes are one pair of 23 present in most cells of the body. Chromosomes contain the genetic material DNA (deoxyribonucleic acid).