What's in a Y chromosome? Researchers mapped what makes males biologically distinct
Two decades after the human genome sequence was completed, researchers have finally finished a map of the piece that makes males distinct.
The Y chromosome is what distinguishes biological males from females. It determines male fertility, including sperm production, and typically is used to determine paternal lineage for tracking inheritance and ancestry.
It was extremely difficult to finish the entire map of the Y because most of the missing pieces were repeats, endless strings of genetic letters saying the same thing over and over again.
Until recently, technology for sequencing genetic material chopped up DNA into bits, read the letters and then pieced the sequence together again. Those long redundancies were nearly impossible to recreate with that kind of technology, said Karen Miga, the University of California, Santa Cruz researcher who co-authored the new study published, in the journal "Nature."
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The good news is humanity now has a complete map. The bad news is it won't make much of a difference.
"Some may have a function but a good deal of this I define as 'hardcore junk,'" said Jennifer Marshall Graves, a geneticist and distinguished professor at La Trobe University in Melbourne, Australia, who was not involved in the research but is familiar with the work.
Still, she said via email, it was "an awesome accomplishment to get all those pesky repeat sequences right, and it will enable us to answer many old questions about how the Y got to be so weird."
More mapping, more opportunities
The part of the Y that has now been sequenced probably has nothing to do with what makes biological males distinctive, said David Page, a biologist at the Massachusetts Institute of Technology and the Whitehead Institute, who has spent most of his career studying the Y chromosome and who conducted the earlier sequencing.
The heavily repetitive segments of the Y chromosome are probably involved in ensuring that that "as the fertilized egg becomes two cells and then four cells and then ultimately, tens of trillions of cells … it's important that they all receive one of the each of the chromosomes that was present in the fertilized egg."
Every human cell typically contains 46 chromosomes, including two that are involved with sex. People who are biologically male have an X and a Y, while females have two Xs, though those who are intersex or have other conditions can have different combinations or numbers of X and Y. The new research did not consider intersex.
In addition to providing a complete sequence of one Y chromosome, a companion paper also included 42 other sequences for comparison and to begin to represent human diversity. Miga, part of a team called the Telomere-to-Telomere (T2T) consortium, is also beginning to compare the human Y sequence to the Y sequence of non-human primates, like chimpanzees, gorillas and bonobos.
"By building more complete maps of human genomes, it gives the research community more opportunities," Miga said, "to better understand what particular genetic compositions make us humans."
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Contact Karen Weintraub at kweintraub@usatoday.com.
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This article originally appeared on USA TODAY: Mapping the Y chromosome, which makes males biologically distinct
