“The size of a chromosome does not correlate with complexity of the sequences within,” Jackson Laboratory professor Charles Lee told BioWorld. Which is why the Y chromosome, which is the runt of the litter as far as human chromosomes are concerned, was the last to be fully sequenced. Now, 20 years after publication of the first near-complete human genome sequence and 16 months after the telomere to telomere (T2T) consortium announced it had completed “gapless assemblies for all chromosomes except Y,” of the human genome, it really is done.