What is it? Why do it?
Genome sequencing is a method of finding the sequence (or order) of the billions of letters that make up a person’s genome. With that information, scientists are able to find and/or rule out crucial genetic disorders before they even show externally.
The Process
The entire genome can’t be sequenced all at once because available methods of DNA sequencing can only handle short pieces of DNA at a time.
So instead, scientists must break the genome into small pieces (1) and then, once they are sequenced (2), reassemble (3) them in the proper order to arrive at the sequence of the whole genome.
Step by step
Step 1 of genome sequencing: breaking up the genome.
- The genome is cut into pieces.
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Step 2 of genome sequencing: each snippet of the genome is individually sequenced (translated to A’s, T’s, C’s and G’s).
How genes are sequenced:
Since these pieces are microscopic, they are not visible (not sequenceable), so scientists have to add enzymes to the DNA segments. These enzymes help produce thousands of copies of each genome piece, making it possible to sequence them.
- Before enzymes are added.
- *Copies are being made*
- Copies are finished.
To read and translate the sequence of these now multiple strands, specially coloured nitrogen bases and enzymes are combined, then added to each segment.These bases bind to their opposites (on the original strand) through complementary base pairing and produce a double-stranded DNA segment with a colourful spot at each letter. Then, scientists take pictures of each piece.
- A specially coloured thymine base is added to the original strand of DNA.
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Step 3 of genome sequencing: Seeing the order of the colours allows them to see which letter bound to which (because A only binds to T and C only binds to G) and therefore read the sequence of the original strand of DNA based on the colour emitted by the opposite bases.
- A machine reads the data and puts the genome pieces back together, in order.
NOTE: Photos are all screenshots from Mark J. Kiel’s “How to sequence a human genome” video. The video is embedded at the bottom of this post.
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Advantages of genome sequencing
• Personalized disease treatments may be possible based not only on the mutant genes causing a disease, but also other genes in the patient’s genome that may otherwise not have been discovered.
• It allows physicians to select the best chemotherapy treatment for their cancer patients and potentially expose them to less toxic treatment by giving them only what they need to fight their disease. This has been the greatest advancement with regards to this kind of biotechnology. As we continue towards the future, the technique will become increasingly better and help many people affected by cancer.
• Scientists will be able to discover disease-causing genes that were previously unknown.
It sounds great! Why would anyone not have their genome sequenced? (Disadvantages)
Some argue that whole genome sequencing can unnecessarily confuse doctors, scare patients and drive up costs. This happens because when a patient learns that they are carrying a gene for a certain health problem or condition, they automatically think that the problem will develop when, a lot of the time, carrying that gene won’t change anything for them (the gene is never “switched on”).
To further explore the helpfulness of genome sequencing, a primary care doctor named Jason Vassy undertook a medical trial in which he sequenced the genomes of 50 patients. He initially expected to find (at most) 1 monogenic disease (a disease caused by a single defective gene), but instead, found 11.
However, almost none of those patients showed symptoms of their supposed genetic diseases. The only exception was a woman with a history of skin rashes, which turned out to be variegate porphyria, a disease that causes attacks that interfere with the function of the nervous system. The other patients were all otherwise healthy 40 and 50 year-olds. They didn’t have the symptoms their genes suggested they should.
It all depends on how desperate you are to know about your DNA. Anyone thinking of sequencing their DNA should ask themselves these two questions:
- Would you be worried about possible developments based on the results?
- Are you willing to pay for the scientific procedure?
Conclusion
I, personally, have a strong belief that whole genome sequencing will have an adverse impact on the world. It will help thousands of people around the world, but if it ever becomes a routine procedure, there will be a lot of unnecessary scares. But who knows? Maybe we’ll surprise ourselves.
Sources
https://www.wired.com/story/you-can-get-your-whole-genome-sequenced-but-should-you/
https://www.cdc.gov/pulsenet/pathogens/protocol-images.html#wgs
https://www.illumina.com/techniques/sequencing/dna-sequencing/whole-genome-sequencing.html
http://www.genomenewsnetwork.org/resources/whats_a_genome/Chp2_1.shtml