Medical researchers out of Murdoch Children’s Research Institute, in Melbourne, Australia have announced their recent discovery about how a baby’s sex is determined, genetically. Or rather, they say it is not just a matter of the X-Y chromosome assignment. As a matter of fact, it is a little more complex than this, and it involves a ‘regulator’ that either decreases or increases the gene activity which determines a male or female fetus.
MCRI researcher and Hudson Institute PhD student, Brittany Croft is the lead author of this study: “Human Sex Reversal is Caused By Duplication or Deletion of Core Enhancers Upstream of SOX9.” She explains that a baby’s sex is in fact, determined by its entire chromosomal makeup at the moment of conception. An embryo that gets two X chromosomes will become a girl and an embryo which inherits the XY chromosome combination will become a boy. This is about as much as we have known already.
More importantly, Croft further describes, “The Y chromosome carries a critical gene, called SRY, which acts on another gene called SOX9 to start the development of tests in the embryo. High levels of the SOX9 gene are needed for normal testis development.”
She goes on to detail that if, however, there is any disruption in the SOX9 activity—and only low levels are present—the fetus will not develop a testis and that will result in a baby that has a sexual development disorder.
Lead study author, Professor Andrew Sinclair, explains, too, that 90 percent of human DNA is actually “junk DNA or dark matter.” Essentially, most of our genetic makeup actually contains no genes whatsoever, but they carry important genetic influences—regulators—which control the influence of our genes.
Sinclair notes that these regulatory segments of our DNA are called “enhancers.” He comments they found three of these “enhancers” which work together to ensure the SOX9 gene is turned on at its highest levels—in an XY embryo—in order to produce normal testis in a male baby.
The study also showed, Sinclair says, XX patients who would otherwise have ovaries (and be biologically female) but carry additional copies of these “enhancers”—which results in higher levels of SOX9 activity—and develop testes instead of ovaries. They also found the opposite to be true.
To conclude, then, Professor Sinclair summarizes we have probably one million enhancers to control 22,000 genes.
This study has been published in the journal Nature Communications.