fretboard wrote: .........so how did the various genotypes come about? Just asking cause that area always confuses me. 
Okay, so I'll try and give this a go from an evolutionary genetics perspective:
As Vororo says HCV has been around for a long time. Basically we probably started out with either one (or
possibly a very few) strain of HCV which crossed the barrier from some other host into the human population. Viruses don't breed though so they basically replicate themselves with each generation being the same as the previous one.
The exception to this rule is when they mutate into something different but in almost all cases the mutation will be weaker than the original strain and won't be as successful at replicating so will die out or be killed off by its hosts immune system ending that new strain before it has a chance to spread into other hosts. But very, very occasionally the mutation will be successful. It will be good at replicating itself accurately and may have an advantage over the original in how it manages to evade our immune system. So it will continue to thrive and may get lucky enough to spread into other peoples bloodstreams. If it does that often enough then that strain will likely continue into the future as a new genotype or subtype. Now, the chances of genotype 1b mutating into 3a are so infinitesimally small that basically "it ain't gonna happen!". But what will happen is that 1a will become 1ax or 1ay or if it is different enough it will create a new genotype, say GT8 or whatever we decide to call it.
Here you have to remember that because HCV is only spread by blood to blood contact it has a linear transmission path so in ancient times you would find that all the people infected in an area would have the same or similar genotypes/subtypes. Until you throw in population movement, migration and now modern jet travel, etc. then we start to get a mix of types across the world.
Below is a great picture that shows the main genotypes by their place of origin/greatest commonality. The interesting thing to note is that while there are 7 main genotypes there are many, many more subtypes. Some of these subtypes have or will die out, other new ones will be created. This is a bit like human genetics in that there are people who are blue eyed, and of these some will have blonde hair. So we have blue eyed/blondes but even within this grouping there will be some with straight hair, some with wavy hair, some with curly hair and some with frizzy hair. Each of the Geno-subtypes is a bit like that. But to keep things simple and because all the genotype 1a subtypes are very similar, we just say they are 1a. (Or blue eyed/blondes).
Hopefully all that makes sense as a very simplistic

explanation. Please discuss amongst yourselves and there will be a test in the morning.