Probability calculus, not calculus in the sense of integration and differentiation.
>So I don't understand your notation
P(x) is the background probability of x. P(x|y) is the probability of x given y.
>I'm not sure if this would compound over generations
It's already had plenty of time to compound over generations, to whatever extent it does.
>the chance for birth defects goes from around 1% to 3-4%, about the same as a woman in her late 30s/early 40s having a child.
Indeed, which shows how silly your theory is. I mean, are you really suggesting that a slightly higher incidence of e.g. cystic fibrosis in Pakistani communities somehow makes it more difficult for them to integrate? That's such utter nonsense that you shouldn't be surprised if people infer some kind of malicious intent behind your comment.