Many experts believed that the sex of the baby was dependent on X-Y chromosomes. However, according to a new study, there is another factor that has a key role to play in determining the gender of the baby. A regulator reduces and increases the activity of genes. Depending on the activity, the gender of the baby is decided.

The researchers conducted a study at Melbourne’s Murdoch Children’s Research Institute. This study was published in the journal “Nature Communications” by Brittany Croft. As believed, the chromosome of the baby determines the sex. An embryo with X-Y make-up results in a boy while XX chromosomes indicate its a girl.

According to Croft, Y chromosome consists of a gene, SRY; it acts on another gene, SOX9. This develops testes in the embryo. She mentioned that for the normal development of testis, high level of SOX9 is required.

When there is an interference in the activity of SOX9 and the levels of this gene are low, the testis will not be developed. This results in a disorder of sex development of the baby.

According to Professor Andrew Sinclair, lead author of the study, 90% of our DNA contains “dark matter or junk DNA”. This means they don’t have any gene instead they carry regulators that decrease or increases the activity of the genes. Such regulators are known as enhancers. He also mentioned any disruption in the control of enhancer can result in sex development disorder.

The main purpose of the study was to understand how enhancer has an impact on SOX9. It also aimed to shed light on the effect of an interruption in the activity of such enhancers.

In this study, they found that 3 enhancers ensure SOX9 gene is on a high level in the XY embryo, which will result in male development and normal development of testis.

They also discovered that XX patients who had ovaries and were female but had copies of 3 enhancers, developed testes. While the XY patients who didn’t have SOX9 enhancers developed ovaries.

In the end, Ms. Croft mentioned that the reversal of sex is caused by losing or gaining these enhancers. So, for the testes and male development, the enhancers that regulate SOX9 gene are crucial. Previously, the studies just focused on the genes to determine the sex. This study is revolutionary because it focuses on the enhancers rather than just the genes.