Scientists have taken an important step forward in understanding the human genome – our genetic blueprint – by completely deciphering the mysterious Y chromosome present in men, an achievement that could help in the study of male infertility, writes Reuters, citing news.ro.

Researchers on Wednesday discovered the first complete sequence of the human Y chromosome, which is one of two sex chromosomes (the other being the X chromosome) and which is normally passed from male parents to male offspring.

It is the last of the 24 chromosomes—the threadlike structures that carry genetic information from one cell to another—in the human genome to be sequenced.

Humans have a pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes, with few exceptions.

Genes on the Y chromosome help control key reproductive functions, including sperm production, formally called spermatogenesis, and are involved in cancer risk and severity. But this chromosome turned out to be difficult to decipher because of its extremely complex structure.

“I would give credit to new sequencing technologies and computational methods,” said Arang Rhee, a research fellow at the US National Human Genome Research Institute and lead author of a research paper detailing the breakthrough in the journal Nature.

“This finally provides the first complete insight into the Y chromosome code, revealing more than 50% of the length of the chromosome that was previously missing from our genomic maps,” said the UC Santa Claus professor of biomolecular engineering. Cruz (UCSC) and study co-author Karen Miga, co-director of the Telomere-to-Telomere Consortium, which was the backbone of the study.

The complete sequence of the X chromosome was published in 2020. But until now, part of the Y-chromosome of the human genome contained large gaps.

“This is particularly important because the Y chromosome has traditionally been excluded from many studies of human disease,” said UCSC genomics and study co-author Monika Chekhova.

“The Y-chromosome is the smallest and fastest chromosome in the human genome, and also the most repetitive, that is, its DNA contains sections of DNA that are repeated several times,” added Chekhova.

The work revealed characteristics of medical regions of the Y chromosome, including a stretch of DNA – the molecule that carries the genetic information for the body’s development and functioning – that contains several genes involved in sperm production. According to the researchers, the new, more complete understanding of Y-chromosome genes is promising for practical applications, including fertility research.

“Many of these genes are important for fertility and reproduction, and especially for spermatogenesis, so being able to catalog normal variations, as well as situations where, for example, azoospermia (absence of sperm in the semen) occurs can be useful for IVF (in vitro fertilization), as well as for further studies of the activity of these genes,” said Chekhova.

In addition to identifying additional genes on the Y chromosome, the researchers discovered that some of the Y chromosome’s DNA had been mistaken in previous studies as being bacterial in nature.

Scientists continue to expand our understanding of human genetics. The first record of the human genome was discovered in 2003. The first complete human genome – albeit with a partial Y chromosome – was published last year. In May, researchers published a new version of the genome that improved the previous one by including a greater diversity of people to better reflect the global population of 8 billion people.

Added to this is the complete sequencing of the Y-chromosome.

“We now have a recipe for fully assembling the Y chromosome, which, although expensive at the moment, could translate into personalized genomics in the future,” Chekhova said.