Eli5: What does it mean to “sequence” a specie’s genetic code (or “genome”) if no two individuals have the same genetic code ?
In: Biology
no two humans are 100% identical; however we are all 99.90% identical and that is useful
a lot of our genetic code, so far, seems to be pretty useless. So if we can figure out what bits of genetic code is useful and what it’s used for we can leverage that knowledge in medicine.
Sickle Cell, cystic fibrosis medicines (others soon) rely on finding and repairing very specific sets of genetic code. More research is showing things like bipolar diabetis has a genetic component that we might be able to one day “fix”
We don’t have identical code but what we do have is the same information ‘fields’, *genes*, in the same places; that’s what they mean by the sequence.
Analogy: If you take me, and some other person from where I am, our driver’s licenses will both have, starting from the top…
* License number
* Condition codes
* Expiry date
* Name
* Address
…and so on. The info in those ‘fields’ will be different for each of us, but you can look on each of our licenses and you’ll find the expiry date, the address, the bar code, etc, in the same locations.
If you look at human chromosome #1, yours and mine, starting on the end of the p (short) tail we will both have the genes for…
* methylenetetrahydrofolate reductase
* C-reactive protein
* interleukin 10
* MTOR kinase
* prostaglandin-endoperoxide synthase 2
…and so on. Our codes for them may or may not be identical – stuff like eye color allows some variation, some proteins are make-this-exactly-right-or-you-die – but barring a pretty funky mutation all humans should have those same genes, on the same chromosomes, in the same order. That ordering is what we call ‘the human genome’.
This is a big deal because if I develop some disease because of not making prostaglandin-endoperoxide synthase 2, they know exactly where the problem is: chromosome 1, p-tail, fifth gene from the end. Some day gene-editing technology will be able to “find and replace” problems like that.
First off, you are right that you sequence an individual and not a whole species–however, species tend to be very close in genetic code, especially compared to other species further out in the tree of life, so an individual can be a very good representative of a species.
Second, to “sequence” something is to literally identify the full “sequence” of genetic code bases (A/C/T/G) making up all the genetic material of that individual’s original code. This might be split up among chromosomes and different locations and such, but most of it is all a linear series of these 4 bases in a specific order.
A “genome” is another word for this full sequence.
Latest Answers