Since the cell contains a total of 6 chromosomes, it has a chromosome number of 6. Each pair is called a homologous pair because they are matching in size and shape. Gender Verification Dividing human cells can be photographed during prophase and metaphase, and all the 46 chromosome doublets can be arranged into 23 homologous pairs. A photographic or digital printed image called a karytype is then made showing all the chromosomes neatly lined up in homologous pairs, from 1 through 23. For example, a person with Down's syndrome would have three number 21 chromosomes rather than two.
Karyotypes can also reveal the gender of a person.
The 23rd pair of males consists of an X and a Y chromosome. The smaller Y chromosome contains a region of DNA on the short arm of the Y responsible for masculinization of the fetus. In females one of the two X chromosomes appears as a condensed, dark-staining Barr body inside the nucleus of somatic cells, near the nuclear membrane. Since Barr bodies only appear in nuclei with more than one X chromosome, they are not present in male cells. Up until the early 1990s, the lack of Barr bodies in nuclei from cheek epithelial cells of women could disqualify them for competition in the Olympic Games.