Healthy human beings have 23 pairs of chromosomes, for a total of 46. Tenty-two of these
pairs, called the autosomes, are probably identical between males and females. The 23rd pair, the sex chromosomes,
differ between males and females. Females have two copies of the X-chromosome, while males have only
one X- and one Y-chromosome.
A trisomy is a form of aneuploidy with the presence of three copies, instead of the normal two, of a particular chromosome. The presence of an extra chromosome 21, which is found in Down syndrome, is called trisomy 21. Other examples of multiple copies of a chromosome are Klinefelter's syndrome, a condition caused by a chromosome aneuploidy. Affected individuals have at least two X chromosomes and at least one Y chromosome. The 48, XXYY (male) syndrome occurs 1 in 17,000 births and has traditionally been considered to be a variation of Klinefelter's syndrome. Foekje Dillema probably had this syndrome. But in 1950 they could not detect this very well and just saw a positive signal for the Y chromosome, so she was banned for life from (female) athletics. Had genetic testing been 60 years further in those days, she probably would have been the greatest Dutch sports person of all time rather than Fanny Blankers-Koen...