An international team made up of more than 100 researchers has managed for the first time to fully decipher the elusive Y chromosome, present in males, a breakthrough that could open up research in fields such as male infertility or the fight against cancer. In this way, ‘Y’ (one of the two sex chromosomes, along with the X), which is passed from father to son, becomes the twenty-fourth and last human DNA chromosome to be sequenced.
Chromosomes are the threadlike structures that carry genetic information from cell to cell. In each of the cells people have two sex chromosomes, XY in males and XX in females. The Y chromosome is in charge of developing reproductive functions, such as sperm production (spermatogenesis), but at the same time it has a highly complex structure. While the complete sequence of the X chromosome was deciphered in 2020, only half of the Y had been ‘read’.
The researchers recall that the structure of the Y chromosome has been difficult to decipher because some of the DNA is organized into palindromes – long sequences that are the same forward and backward – spanning up to more than a million base pairs. Furthermore, a large part of the Y chromosome that was missing in the earlier version of the Y reference is satellite DNA, that is, large, highly repetitive regions of non-protein-coding DNA. On the Y chromosome, two satellites are entwined with each other, further complicating the sequencing process.
This achievement has now been possible thanks to “new sequencing technologies and computational methods,” explains Arang Rhie, a scientist at the US National Human Genome Research Institute and lead author of the study, published in the journal Nature.
Scientists have obtained the complete sequencing of 62,460,029 base pairs of the Y chromosome, which is 30 million more than those previously revealed. In addition, they have revealed the complete structures of several families of genes, have identified 41 new protein-coding genes, and have corrected errors in studies of the Y chromosome that were available up to now.
The finding has important practical applications. When scientists and doctors study an individual’s genome, they compare their DNA to a reference standard to determine where there are variations. But until now, they ran into a problem in the Y chromosome. “The Y chromosome part of the human genome contained large gaps that made it difficult to understand the variations and associated diseases,” the consortium members stress. With the new discovery, this obstacle may be overcome.
“The first complete view of the Y chromosome code is finally available, revealing more than 50% of the length of the chromosome that previously did not appear in our genomic maps,” says the professor of biomolecular engineering at the University of California at Santa Cruz (UCSC) and co-author of the study, Karen Miga, co-director of the Telomere-to-Telomere (T2T) consortium, responsible for the research.
“By having this 100% complete sequence of the Y chromosome, we can identify and explore numerous genetic variations that could be influencing human traits and diseases in a way that we have not been able to do before,” concludes another co-author, Dylan Taylor, geneticist and doctoral student at Johns Hopkins (United States).
Knowledge of the Y chromosome will allow us to know if some of the most prevalent diseases or cancers in men can be attributed to a genetic origin, and not to less healthy lifestyles in terms of diet, exercise or stress.
“A few years ago, half of the human Y chromosome was missing, the complex and difficult satellite zones,” says Monika Cechova, co-lead author of the paper and a UCSC postdoctoral fellow in biomolecular engineering. “Back then we didn’t even know if it could be sequenced, which was puzzling. This breakthrough is a huge change.”
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