Scientists study how differences between sexes develop in animals

Scientists looking into the intricate world of sex differences have uncovered significant insights into how these evolve.

They found that in animals, sex differences differ very dramatically across species, organs and even developmental stages.

Additionally, they saw that the evolution of these differences at the gene level is more rapid, while at the level of cell types, it is gradual.

The study findings were published in the Journal Science on November 2.

Understanding sexual dimorphism

The study focused on examining sex-based disparities in multiple species, including humans, mice, rats, rabbits, opossums, and chickens. Their focus was on the development of five key organs: the brain, cerebellum, heart, kidney, and liver.

Notably, they highlighted contrasting patterns of sexual dimorphism in different species, with certain organs displaying more pronounced differences between the sexes than others.

Key findings

The researchers observed that while organs developed, few sex differences were apparent. However, around the time of sexual maturity, they observed that disparities intensified significantly.

"We found that the levels of sex-biased expression varied substantially across organs and species. Across mammals, sex-biased expression was rare during organ development. In organs with high levels of sex-biased expression, the differences between the sexes only appeared around the time of sexual maturity."

Moreover, the study revealed that only a few genes that are different between males and females are the same in all animals, and theseare mostly on the sex chromosomes (X and Y).

Even though different animals have different genes that are different between males and females, the researchers noticed that the same kinds of cells show differences in all the animals.

For example, even though mice and rats have different genes in their livers, the genes that are different are in the same kind of cell in the liver. This is important because it helps us understand how differences between males and females can affect things like how the body processes medicine.

"Sex-biased expression evolved quickly across species between orthologous genes. However, the cell types responsible for most sex-biased expression were the same across species."

Commenting on the findings, Leticia Rodríguez-Montes, a PhD student at Heidelberg University, noted the intriguing discovery that a small set of genes on the sex chromosomes are different between males and females in all the animals they looked at.This could potentially serve in the understanding of fundamental genetic triggers for sex-specific traits.

(With inputs from agencies)