Having a bad gene is not someone's fault, the best that you can say is 'bad luck'. If it is severe and you know that you have it, then maybe you should think hard before you have children.
Yes, you almost have it concisely there: Having a bad gene is bad luck, and choosing to breed if you have it is someone's fault.
Some people with genetic problems do do that, or have the foetus tested and aborted if it has the problem.
I just don't think I've got great genes or a great situation for being a good parent, so even though I think I'd be better than the average dillhole I still don't think that raises the bar sufficiently to call myself a good parent. Thus, I'm not having any. I've had multiple opportunities, and my last girlfriend even left me for someone else over it. It was sad, but that's preferable to having her skipping pills trying to catch my child, so I'm not really complaining. Now, how can I make a statement similar to "I'm putting my money where my mouth is" without making it sound like I'm sucking my own dick? If I could do that, I've have been all over pornhub already.