Scientists have gained significant insights into the evolution of sex differences, with their study revealing variations across species, organs, and developmental stages. Published in the journal Science, the research focused on sexual dimorphism in various species, including humans, mice, rats, rabbits, opossums, and chickens, with a specific emphasis on the brain, cerebellum, heart, kidney, and liver.
The findings indicated that sexual differences in gene expression levels vary greatly between organs and species. Notably, sex-biased expression was infrequent during organ development, but these differences became more pronounced around the time of sexual maturity.
The study also highlighted that only a few genes exhibit sex-based differences that are consistent across all animals. These genes are primarily located on the sex chromosomes (X and Y). However, the researchers observed that the same types of cells display differences between males and females in all the animals studied, even though the specific genes involved may differ.
For instance, while mice and rats may have different genes in their livers, the genes that differ are found in the same type of liver cell. This observation is significant as it aids in understanding how sex-based differences can impact processes such as drug metabolism.
The research suggested that sex-biased gene expression evolves rapidly between species when considering orthologous genes. Nevertheless, the cell types responsible for most sex-biased expression remained consistent across species.
Leticia Rodríguez-Montes, a PhD student at Heidelberg University, noted the intriguing discovery of a small set of genes on the sex chromosomes that exhibit differences between males and females in all the animals studied. These findings could potentially contribute to a deeper understanding of the fundamental genetic triggers for sex-specific traits.
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