Hey, they've got at least one biologist on the team, I'm sure they can figure it out in a way that works reasonably
Speaking as
also a biologist, I would expect bloodline/non-bloodline crossbreeds to mostly be stillborns.
Take Iron Nerve, for example. It directly fucks with your brain and peripheral nervous system. Who knows what happens if you're heterozygous for something which causes a such
major change to your brain development? I ain't touching
that mess with a ten-foot scalpel. You could easily end up with babies that are completely paralysed and die upon birth because they can't move their intercostal muscles in order to breathe. Frozen Skein is arguably worse. Halfblood Moris might end up lacking important brain regions, or getting duplicate regions that squash the parts that are supposed to be there so they don't have room to properly develop. Or just getting a slight problem with their synapses that mean they can't fire, and the kid is born braindead.
Genetics gets
really dark when you fuck with it. It can be really hard to predict what's going to happen when you mix sufficiently different genomes. If you're lucky, you get mules. If you're still kinda lucky, you get Cnemidophorus
neomexicanus (an all-female species of hybrid lizards which can only reproduce by parthenogenesis because there are no males). But that's only if the species are close enough together that the alleles mostly have direct counterparts in the mate's species. With bloodlines, you might be dealing with a situation where
that isn't true, and then things get real fucking messy.
If I was the QMs I would say bloodline inheritence runs on chakra-magic, not DNA.
E: Though I feel I should say as a disclaimer that this sort of thing isn't something I've looked into in much detail, and I
could be wrong on points.