Scientists identify the chromosome that makes humans so unique

At least three microRNA gene families discovered on chromosome 21 are not shared with any other primates and may have played important roles in unique human evolution.

A team at the City University of New York used genome alignment tools to compare the most recent drafts of the human and chimpanzee genomes, meticulously searching for new genetic elements unique to humans. Starting with the smallest human chromosome, chromosome 21, the researchers were surprised to find , which harbors several orphan microRNA genes. The results are published in the American Journal of Biological Anthropology.

Although the team found that the long arm of human chromosome 21 aligns well with that of other extant ape species, the short arm aligns poorly, suggesting that this region of the human genome has recently and substantially separated from that of other extant apes. primates.

According to his analysis of prehistoric human genomes, . The genes also show little or no sequence-based variation within the modern human population. Therefore, the team theorized that the microRNA (miRNA) genes found in that region [miR3648 y miR6724] they probably evolved in the time since the chimpanzee and human lineages split, sometime in the last seven million years, and are specific to humans.

Using computational tools, the team found with a high degree of probability that the predicted genetic targets of the relevant miRNAs are related to embryonic development. Both miR3648 and miR6724 have been detected in tissues throughout the human body, including the brain, and the findings point to the intriguing idea that these microRNA genes contributed to the distinct evolution of our species and the uniqueness of humanity.

“Understanding the genetic basis of human uniqueness is an important task because, despite sharing almost 99% of our DNA sequences with the chimpanzee, we are remarkably different organisms.” said the student researcher participating in the study José Galván. “Small post-transcriptional regulatory elements such as miRNAs and siRNAs (small interfering RNAs) are underestimated and often misunderstood in the effort to understand our genetic differences.”

Thanks to their small size and structural simplicity, miRNA genes have fewer barriers to creation de novo than other types of genes. MicroRNA genes can be extremely prolific in regulating other genes, meaning that modest changes in DNA sequence can have far-reaching effects on the human genome. The creation of miR3648 and miR6724 are excellent examples of this process.

This study revealed a new possible mechanism for the creation of new miRNA genes through rRNA gene duplication, requiring further investigation on how general this phenomenon may be.