There are obvious differences between males and females but what difference do genes make? In a first-of-its-kind study, researchers from Indiana University (IU) have studied the genetic mechanisms between these differences and have discovered how the “master gene” attributes the right physical trait to the right sex.
The master gene, called doublesex or simply dsx, is responsible for the different traits exhibited by male and female members of the same species. The master gene, sometimes called master switch, is a single gene that activates a myriad of other genes leading to the development of tissues. One example of a master gene is Pax-6, the gene that is responsible for the development of eyes.
A human genome contains about 19,000 to 20,000 genes. The first-of-its-kind study looks at dsx’s role across the whole genome and solves the riddle about how the master gene controls the assignment of characteristics to the right sex. However, further research is warranted.
“We want to know more about this gene because it helps us answer a major question about development and evolution: How do animals with similar genomes — such as males and females of the same species — produce different versions of the same trait? And why do some traits, like ornamental features that attract mates, vary so widely, while others, like legs, don’t?” said Cris Ledón-Rettig, a postdoctoral researcher at Indiana University and the lead author of the study.
The researchers noticed that master gene is not simply the switch to turn on and off male and female characteristics but it plays a major, albeit highly complex, role in controlling the expression of different characteristics in both sexes at several points in the genome.
Researchers studied the effects of dsx in the male beetle Onthophagus Taurus and found the gene to activate several other genes that promote specific sex functions. For instance, dsx activates different genes that promote development of genitalia in both sexes. If the master gene is tweaked, it can lead to female genital development in male and vice versa.
Researchers also found that dsx performs its function just so precisely by activating the right genes. Remember, a small tweak in the gene can lead to major changes that could travel to generations.
For the study, the IU researchers divided the beetles into two groups; group A contained normal beetles, while group B contained beetles with suppressed genes. Master gene was found to affect over 250 and 1,000 points on the genome in normal male and female beetles.
In simple words, the researchers found that master gene possesses powerful abilities to affect gene expression across the whole genome in both males and females of all species.
An interesting find of the study was that the master gene selects a particular trait, for instance development of genitalia, and instructs “subordinate genes” to develop the male and female versions of it.
Dsx also functions to inhibit development of male characteristics in females and vice versa. This is a critical function and a buffer trait that prevents development of unwanted characteristics in a species.
Take the beetle’s example. The male beetle has large horns to battle rivals and to win the mate. It is dsx controlling the development of specific male characteristics.
The researchers studied the effect of dsx on one particular trait – head horns – and found the master gene to target the exact same gene in both sexes, but only in reverse direction. In males, it led to the development of elaborate horns and a complete absence of horns in females. When researchers “switched off” dsx, it led to the development of “intermediate sized horns” in both males and females.
The effects of master gene vary from species to species. In birds, for instance, dsx activates genes that determine male characteristics, such as a surplus of testosterone, the male hormone. It is testosterone that attributes “aggressive” behavior to males. The aggressive and dominating behavior in turn helps win mates.
The effects of master gene are similar in humans. The study was published today in Nature Communications.