How scientists fully solved the Y chromosome mystery

Here’s a quick throwback biology lesson – humans typically have 46 chromosomes, which store genetic info in our cells. Sex is (mostly) determined in humans through the X and Y chromosomes. Traditionally, it’s believed that there were two possible combinations, XX (female) and XY (male). As scientists continue to research chromosomes and sex, they’ve accepted that things aren’t quite that black and white. For some people, their sex chromosomes may say one thing, but their sexual anatomy is actually completely different. And some people even end up with three X chromosomes or a missing X chromosome.

Genetic science teams have been trying to figure out the Y’s origins in evolution, how it affects male fertility and how it’s linked to certain diseases. For over 20 years, they’ve been working on sequencing the Y chromosome. In fact, every human chromosome except the Y had been fully mapped by 2022.

Even though it’s the shortest chromosome, the Y is sprinkled all over with repetitive DNA strings. Usually, DNA is sequenced by getting short reads from different areas of a chromosome, and patching them into a single sequence where there’s overlap in the DNA strings. But, repetitive DNA makes this whole process almost impossible.

But, finally, researchers have mapped out the Y chromosome. They used the latest full sequencing tech, which allows them to read thousands of DNA bases very quickly. Last week, a group of researchers from the Telomere-to-Telomere (T2T) Consortium published a breakthrough study in the journal Nature, finally revealing what the Y fully looks like.  

"This is especially important because the Y chromosome has been traditionally excluded from many studies of human diseases," UCSC genomicist and study co-author Monika Cechova said. "The Y chromosome is the smallest and the fastest-evolving chromosome in the human genome, and also the most repetitive.”

This new work shows the DNA involved in sperm production, which is valuable in fertility-related research. Researchers also discovered that some DNA from the chromosome had been mistaken as bacterial in earlier studies.

“Research is emerging that shows proper Y chromosome gene function is incredibly important for the overall health of men,” said Charles Lee, a senior author on the study and professor and research director at the Jackson Laboratory for Genomic Medicine. “Our study enables the inclusion of the full Y chromosome in all future studies when sequencing male genomes to understand health and disease.”