DAZ

• It’s also small and seriously weird; it carries few genes and is full of junk DNA that makes it horrendous to sequence.
• However, new “long-read” sequencing techniques have finally provided a reliable sequence from one end of the Y to the other.

Making baby boys

• The embryonic testes make male hormones, and these hormones direct the development of male features in a baby boy.
• Female hormones then direct the development of female features in the baby girl.

A DNA junkyard

• It is smaller and bears few genes (only 27 compared to about 1,000 on the X).
• The Y also has a lot of DNA sequences that don’t seem to contribute to traits.
• This last DNA class occupies big chunks of the Y that literally glow in the dark; you can see it down the microscope because it preferentially binds fluorescent dyes.

Why the Y is weird

• We have a lot of evidence that 150 million years ago the X and Y were just a pair of ordinary chromosomes (they still are in birds and platypuses).
• Then SRY evolved (from an ancient gene with another function) on one of these two chromosomes, defining a new proto-Y.
• Read more:
  Men are slowly losing their Y chromosome, but a new sex gene discovery in spiny rats brings hope for humanity

Sequencing Y was a nightmare

• They’ve done this using short-read sequencing, which involves chopping the DNA into little bits of a hundred or so bases and reassembling them like a jigsaw.
• But it’s only recently that new technology has allowed sequencing of bases along individual long DNA molecules, producing long-reads of thousands of bases.

So what’s new on the Y?

• A few new genes have been discovered, but these are extra copies of genes that were already known to exist in multiple copies.
• The border of the pseudoautosomal region (which is shared with the X) has been pushed a bit further toward the tip of the Y chromosome.
• But perhaps the most important outcome is how useful the findings will be for scientists all over the world.