"More than 20 years ago, the human genome was first sequenced. While the first
version was full of “holes” representing missing DNA sequences, the genome has
been gradually improved in successive rounds. Each has increased the quality of
the genome and, in so doing, resolved most of the blank spaces that prevented
us from having a complete reading of our genetic material.
The fundamental difficulty researchers faced in reading the genome from end to
end is the enormous number of repeated sequences that populate it. The 20,000
or so genes we humans have occupy barely 2% of the entire genome. The remaining
98% is essentially made up of these families of repeated sequences, mobile
elements known as transposons and retrotransposons, and – to a lesser but
functionally important extent – gene expression regulatory sequences. These
function as switches that determine when and where genes are turned on and off.
In March 2022, a major revision of the genome was published in the journal
. An international consortium of researchers known as “T2T” (telomere
to telomere, which are the ends of chromosomes) used a novel strategy based a
type of cell (CHM13) that retains only one copy of each chromosome.
Combined with the latest techniques for sequencing DNA, the researchers managed
to add some 200 million letters to the human genome, resolving most of the
holes in chromosomes 1 to 22.
The only one left out was the smallest of all the chromosomes we humans have:
Y. It’s an exclusively male chromosome that is also the most complex, with
repeated sequences of all kinds."
*** Xanni ***
Chief Scientist, Xanadu
Partner, Glass Wings
Manager, Serious Cybernetics