Okay, so we had a bit of a chat in admin to make sure we worded this properly and didn't wander off into confusingness like that paper is unless you've studied a fair bit of science xD
So firstly, magic is hereditary. We decided to forego the term "genetic" because that implies there's one or two specific genes that are responsible for it - and as we know from experience, you can't actually explain it being both dominant and recessive with simple punnet squares, it's rather more complex than that. However, the word "genetic" theoretically carries the possibility that muggle scientists could splice in the magic gene into an otherwise muggle zygote and produce magical offspring, which obviously doens't fit with the setting.
But I'm digressing already! So magic is inherited...you can perhaps think of it as something like height. So two muggles are most likely to have a muggle kid (as in, two short parents have a short kid) but they *might* have a magical/tall kid (because great-granddad Bert was a wizard/6'4). Purebloods will almost always have magical children but occasionally something happens and they have a squib (tall parents almost always have tall children, but very occasionally the child is extremely short). If the purebloods are inbred the chances of this happening would be increased (this can be likened to the fact that cousins marrying cousins often leads to genetic diseases etc)
However it's a bit more complicated, because magic is some kind of innate vital force that can be channelled in various ways. Allowing me to be vain for a moment; my singing ability which was there long before I had lessons, so it's obviously neither entirely taught nor entirely hereditary. It's also not something you could isolate and say "Right, that's it. There. The "singing" gene." So there are varying degrees of magic, accounting for why some wizards are incredible at wand work and others, to paraphrase Flitwick, resemble a baboon wielding a stick.
Onto muggle illnesses, and vice versa. The best parallel I managed to draw is a little hazy, but there are cases of women in certain parts of Africa who haven't contracted HIV despite working as prostitutes for years and having had sex with people who have AIDS. Sorry to bing something so RL into things, but I can't find a better analogy. Because these women evidently have some sort of natural immunity that most folks lack. So drawing on from that sort of thing, wizards might have a much lower probability of developing a cancerous tumour; perhaps when it happened it would develop so slowly that old age would generally take them first. On the other hand, a muggle will never get spattergroit because they have natural immunity.
Magical cures would relate to serious diseases - so there's no magical cure for the common cold any more than there's a muggle one. They just have potions they can take to ease the symptoms.
We also wouldn't say the wizarding world is behind the muggle one in terms of technology. That's somewhat like saying a degree in literature and philosophy is less worthwhile than one in maths. They're just different, and they operate in a different way. Wizards had international travel sooner and far more easily than muggle, for example. And there's nothing in the muggle world that the magical world doesn't have as well, apart from TV and cinema. And personally, I'd argue that if you could entertain yourself with magic, you wouldn't need the TV anywyay. Though I do feel sorry for wizards who don't get to watch Dr Who.
OMG, Dr Who! Tomorrow Night! New Doctor! *runs off excitedly*
I'm sorry, where was I..?
Hope that helps a bit and makes sense!
[carys]~ The Admin Team