The tech that made this possible is really cool. They force DNA through a teeny-tiny hole in a protein, and measure changes in voltage to ID each individual letter.

Totally different from traditional shotgun sequencing!

Tl;dr: was difficult due to repetitive structure. Will enable further research.

The achievement completes the Y chromosome's genetic code and unveils key details that could provide a crisper picture of the role the chromosome plays in male-specific development, fertility, and genetically triggered diseases like cancer