After the structure of DNA became known, it was obvious that research would be done to determine its exact composition.
By 1977, a method had been published to determine the sequence of nucleotides in DNA. Ten years later, in 1987, the first machine to automate this work hit the market (Venter 2001).
The fact that chromosomes had not proven to be a perfect indicator of people’s sex and gender identity was all the more reason to look for genetic evidence of the difference between men and women. A 1990 publication introduced a new gene that was confidently called the SRY gene: Sex Determining Region Y (Sex Determining Region [on the] Y-[chromosome]) (Sinclair 1990).
In 1991 they had already decided to use the SRY gene in the sex test at the Olympic Games from then on. Because the SRY test also proved not to be useful, it was decided in 1991 to stop such sex tests (Ritchie 2008).
Also, in the search for genetic evidence for the cause of different forms of sex diversity, the results were not universally applicable. For example, several research groups, including one in the Netherlands, worked on information about the Androgen Receptor gene in the late 1980s (Brinkmann 1989). By mapping the Androgen Receptor gene, for example, it became possible to determine in girls with XY chromosomes whether they had androgen insensitivity syndrome or yet another form of sex diversity. But again, there appeared to be more exceptions than expected.
Even in 2018, no genetic variation can be found in about half of the people affected by a form of 46,XY sex diversity (Cools 2018). A 2012 review article providing insight into the large number of genes involved in different forms of sex diversity even states that genetic variation was found in 20 percent of cases (Ono 2012). In other words, genetic testing can make a diagnosis with certainty, but cannot exclude a diagnosis with certainty.