First complete human genome mapped by scientists

By Mark Waghorn via SWNS

More than 20 years after they started, the human genome has finally been mapped by scientists.

It contains over six billion 'letters' contained in our DNA code but scientists have taken two decades to decipher the last eight percent.

Knowing them opens the door to exploring everything that is genetically determined and will shed fresh light on diseases, intelligence - and looks.

Genes control eye and hair color, height - and even the size of your nose.

The breakthrough is a "Rosetta stone" for understanding complex mutations underlying illness and evolution.

In 2003, a revised draft was published - which was missing more than eight percent. The hard-to-sequence long stretches were the most complex - full of repeating letters.

They were impossible to decipher with the technology at the time. Now an international team finally has.

Lead author Dr. Adam Phillippy, of the University of Maryland, said: "In the future when someone has their genome sequenced, we will be able to identify all of the variants in their DNA and use that information to better guide their healthcare."

"Truly finishing the human genome sequence was like putting on a new pair of glasses.

"Now that we can clearly see everything, we are one step closer to understanding what it all means."

It has been described as the 'book of life.' Co-author Professor Evan Eichler, of the University of Washington, Seattle, said: "We are seeing chapters that were never read before.

"It turned out many of the regions I was interested in were in the gaps."

He added: "Ever since we had the first draft human genome sequence, determining the exact sequence of complex genomic regions has been challenging.

"I am thrilled that we got the job done. The complete blueprint is going to revolutionize the way we think about human genomic variation, disease and evolution."

The Human Genome Project has taken more than two decades and cost $3 billion (£2.3bn).

Former leader Prof Robert Waterston, also from Washington who was not involved in the new effort, said: "There are no longer any hidden or unknown bits.

"I think that is psychologically a big thing. I just admire these scientists for sticking with it."

The human genome is made up of just over six billion individual letters of DNA - about the same number as other primates like chimps.

They are spread among 23 pairs of chromosomes. To read a genome, scientists first chop up all that DNA into pieces hundreds to thousands of letters long.

Sequencing machines then read the individual letters in each piece, and scientists try to assemble them in the right order, like putting together an intricate puzzle.

Most cells contain two genomes ­– one from the father and one from the mother.

Prof Eichler explained: "We came up with the idea of getting a complete genome by sequencing just one of the genomes instead of solving two at the same time."

Other key advances included rapid improvements in Oxford University's gene sequencing machines that can accurately read a million letters of DNA at a time.

Dr. Phillippy said: "We had the benefit of youthful optimism and we were fired up by the promise of these new technologies."

The machines ran non-stop for six months - with scores of scientists assembling the pieces and analyzing the results.

They got a boost when California-based Pacific Biosciences introduced a new sequencer that generated 'long-reads' that were greater than 99 percent accurate.

By the summer 2020, the consortium had two chromosomes and planned a 'hackathon' to get the other 21 - working remotely over Zoom and Slack during the pandemic.

Dr. Philliphy said: "It is a whole new treasure chest of variants we can study to see if they have functional significance."

Complex gene patterns may have helped create the human species - and explain our rapid evolution.

Some associated with bigger brains are highly variable, said Prof Eichler. One person might have 10 copies of a particular gene, and others only one or two.

This can spell trouble during fertilization when chromosomes from mum and dad line up and swap pieces. The mismatched genes can lead to 'an earthquake' of alterations.

Prof Eichler explained: "These regions become a crucible for both rapid evolutionary changes and disease susceptibility, both within and between species."

Consortium members are now working to sequence a genome with different chromosomes inherited from each parent.

They are also beginning a pan-genome effort to read the entire DNA sequences of hundreds of people from around the world.

Added co-author Prof Erich Jarvis, of Rockefeller University, New York: "The goal is to create as complete a human genome as possible, representing much more of human diversity."

The study is reported in six papers in the prestigious journal Science.