Eli5: What does it mean to “sequence” a specie’s genetic code (or “genome”) if no two individuals have the same genetic code ?

Question

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

Answer 1

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.