A team of almost one hundred researchers from around the world have published the first entirely complete sequence of the human genome.
Previously in 2003, the Human Genome Project sequenced roughly 90 to 92 per cent of the human genome. The remaining eight per cent had eluded complete sequencing for decades as the DNA in some regions overlapped and repeated, making it difficult to piece together. Now, the Telomere-to-Telomere (T2T) Consortium published a sequence on March 31 which they say includes those hard-to-pin-down areas of the genome.
“Two decades ago, we really celebrated the first release of a human reference genome, and that has just been transformative for human, genetic and genomic research,” T2T consortium co-lead Karen Miga said in a video release. “ … We’re now releasing to the public over 200 million bases of sequences that have never been seen before.”
Sequencing the human genome like an impossible puzzle
To sequence the billions of base pairs that make up the human genome, scientists would sequence small sections and later piece together the data like a jigsaw puzzle. This was difficult to do in areas that heavily repeated themselves — like the infamous Schmuzzle puzzle of the ’80s made up of identically shaped pieces, it would be alarmingly easy to fit together two pieces that don’t actually go.
Advancements in technology allowed researchers to capture a much larger stretch of the DNA than before, and then zoom in to ensure the accuracy.
The team has now set their sights on coding a panel of genomes that will reflect the “genetic and genomic diversity around the world.”
All in the genes
Our genetic code is found in DNA: long strings of chemical building blocks bundled together and mostly stored in the nucleus of every cell. Each building block contains one of four different chemicals, called nitrogen bases, that link together to create a code. Sections of this code make up the blueprints for different proteins used by the body — like the proteins that make up blue versus brown eyes, different types of muscle fibres, curly versus straight hair, et cetera.
Sequencing the genome refers to deciphering which nitrogen base is found where in the code, writing out the sequence that researchers then attempt to translate to known proteins. This entire process can be arduous, but some scientists hope that in the future patients will be able to have their entire genome sequenced quickly and cheaply, taking us that much closer to personalized medicine.
What was the missing piece of the human genome?
The long sections of DNA are packaged into chromosomes: bundles of genetic code that are unwound and translated as needed. Most humans have 23 pairs of chromosomes, one set each from the mother and father, that contribute to the uniqueness of each person.
The majority of the DNA that was unsequenced was located on the long, trailing ends of five of the chromosomes (called telomeres) and the dense middle section of the chromosomes called centromeres. Unpacking the telomeres and the centromeres is important, as although they contain more repeating code than actual decipherable genes, they are believed to play important roles in certain medial conditions.
“Understanding the centromere as a unit is needed to fully understand errors in chromosome movement when cells divide, which is thought to be a driver in cancer and some other human diseases, including birth defects,” Dr. Steven Henikoff, a molecular biologist at Fred Hutchinson Cancer Center, told Medical News Today. “So finishing the job of sequencing the human genome is important not only because it’s needed to fully understand a central problem in genetics, but also because of the importance of centromeres in human health and disease.”
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