Study reveals how a baby’s sex is determined

A new study has revealed that a baby’s sex is not just about the X-Y chromosomes, but involves a ‘regulator’ that increases or decreases the activity of genes which decide if a baby becomes male or female. An embryo with two X chromosomes will usually become a girl, while an embryo with an X-Y combination results […]

A new study has revealed that a baby’s sex is not just about the X-Y chromosomes, but involves a ‘regulator’ that increases or decreases the activity of genes which decide if a baby becomes male or female.

An embryo with two X chromosomes will usually become a girl, while an embryo with an X-Y combination results in a boy, however  Medical researchers at Melbourne’s Murdoch Children’s Research Institute with the new study have given more insights on the regulator and disruptions during sex development.

One of the researchers, Ms Crost said, the Y chromosome carries a critical gene, called SRY, which acts on another gene called SOX9 to start the development of testes in the embryo. High levels of the SOX9 gene are needed for normal testis development.

“However, if there is some disruption to SOX9 activity and only low levels are present, a testis will not develop resulting in a baby with a disorder of sex development.”

Lead author of the study, Professor Andrew Sinclair said, 90 percent of human DNA is made up of so called ‘junk DNA or dark matter’ which contains no genes but does carry important regulators that increase or decrease gene activity.

He said these regulatory segments of DNA are called enhancers adding that if these enhancers that control testis genes are disrupted it may lead to a baby being born with a disorder of sex development.

Professor Sinclair, who is also a member of the Paediatrics Department of the University of Melbourne said, this study sought to understand how the SOX9 gene was regulated by enhancers and whether disruption of the enhancers would result in disorders of sex development.

He said importantly, we identified XX patients who would normally have ovaries and be female but carried extra copies of these enhancers, (high levels of SOX9) and instead developed testes. In addition. “We found XY patients who had lost these SOX9 enhancers, (low levels of SOX9) and developed ovaries instead of testes,” he said.

Professor Sinclair said that across the human genome there were about one million enhancers controlling about 22,000 genes.

Ms Croft said, “This study is significant because in the past researchers have only looked at genes to diagnose these patients, but we have shown you need to look outside the genes to the enhancers.