"Gender verification of female athletes has long been criticized by geneticists, endocrinologists, and others in the medical community. Problems include invalid screening tests, failure to understand the problems of intersex, the discriminatory singling out of women based only on laboratory results, and the stigmatization and emotional trauma experienced by individuals screened positive."(Excerpt taken from "Gender verification of female Olympic athletes" https://pubmed.ncbi.nlm.nih.gov/12370551/)
There are a variety of birth defects, affecting perhaps one person in 500, that can cause a discrepancy between chromosome composition and sex. The degrees and physical manifestations vary greatly, but there is little to indicate that it gives an athlete a competitive advantage.
From Campbell Law Observer: "Gender verification or “sex testing” as it is colloquially known, first began in the 1960’s. However, as early as the 1930’s, the media began fueling the idea that men disguised as women were competing in women’s sports competitions, rigging the system by unfair competition. Beginning at the Rome Olympic games in 1960, the International Amateur Athletics Federation (IAAF) began implementing rules of eligibility for women athletes. Tests were initially a physical examination but because this was widely resented, sex chromatin testing was later introduced. This type of testing was premised on the principle that women have a single X-chromatic mass, whereas males have a Y-chromatic mass. It sounds simple enough. If a woman was tested and had a Y-chromatic mass, she was a male and excluded from the sport.
That process, however, was deeply flawed. In addition to the risk of contamination and incorrect test results that stemmed from inexperienced workers, the greater problem was that some women possess male chromatin patterns. When such an abnormality exists, the woman is called phenotypic. This condition has little bearing on whether or not an individual is male or female. It simply tests the genetics of the individual –- not the anatomical or psychosocial status of that person. Over the years, the types of testing have changed but not improved. It is generally known and accepted that doping enhances performance in both males and females, but whether too much testosterone in the female body has the same effect, is hotly debated. (http://campbelllawobserver.com/gender-verification-testing-for-female-athletes-humiliating-or-necessary/)
These tests are cruel and discriminatory. There are a lot of women out there with a Y chromosomes, and there are a lot of men without a Y. What these tests do is leave behind tragedies.