Scientists have, for the first time, fully sequenced – or mapped – the Y chromosome. An international group of scientists from the Telomere-to-Telomere Consortium recently completed the painstaking work of study on the one chromosome that determines if someone will be a man or a woman, male or female.
The complete X chromosome sequence was published in 2020.
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And this was no easy task. The Y chromosome has 62,460,029 base pair sequences of a human Y chromosome (the building blocks of DNA)
Everyone has at least one X chromosome, whether you are male or female. But women have two. And only men have the Y chromosome. And it is much smaller than the X chromosome, representing almost 2% of the total DNA in a male cell. The human Y chromosome contains over 200 genes, at least 72 of which code for proteins. Traits that are inherited via the Y chromosome are called Y-linked traits, or holandric traits.
When a sperm cell fertilizes an egg cell, the sperm cell contributes either its X chromosome or its Y chromosome to the fertilized egg. If the sperm cell contributes its X chromosome, the resulting child will be female. If the sperm cell contributes its Y chromosome, the resulting child will be male.
The Y chromosome is constantly shrinking. This is because the Y chromosome does not recombine with the X chromosome during meiosis, the process by which cells divide to produce gametes (sex cells). This means that the Y chromosome is not able to repair mutations that occur in its genes. As a result, the Y chromosome is slowly losing genes over time.
The scientists themselves were amazed by their accomplishment in mapping the Y chromosome.
“It was the Y chromosome that lacked the most sequences from the previous reference genome,” lead author Arang Rhie, a staff scientist at the National Human Genome Research Institute, said. “It was always irritating knowing we were missing half the Y whenever we tried to do any reference-based analysis. I was really excited to curate the first complete Y, to see what we were actually missing, and what we can now do.”
“We didn’t even know if it could be sequenced, it was so puzzling,” says University of California biologist Dr Monika Cechova, who co-led the research. “This is really a huge shift in what’s possible.”
“We didn’t know what exactly made up the missing sequence,” added Dr. Adam Phillippy, head of the Genome Informatics Section at the National Human Genome Research Institute. “It could have been very chaotic, but instead, nearly half of the chromosome is made of alternating blocks of two specific repeating sequences known as satellite DNA. It makes a beautiful, quilt-like pattern.”
