I personally believe that crossbreeding between the races is absolutely possible. I don't think they would kill this in the lore. That would be more regressive than forbidding same-sex marriage, which we know they aren't doing. As mentioned elsewhere, it could be implied from the Mail Moogle quests that Baderon's daddy is a Roe. Considering the Roe population of Limsa, this would not be surprising. It just may be that some racial traits tend to be more prominent than others. This kind of genetics is also true in the real world. The only race with significant dimorphism from the standard human physiology is Roegyden. It could very well be that their genetic traits tend to be more regressive than the others, which could explain why people who appear to be of a specific race may have Roe ancestry and not show it. As for G'eras eye... Despite what the clones said about being sterile, I have a feeling that G'eras line having the eye isn't natural. Pure speculation. Based on how uncommon hetrochromia is in the first place, and the fact that G'eras talks about the Allagan EYE singular. The clones didn't have heterochromia, which means this feature either entered the Allagan Royal Line at some other point or is, perhaps, a feature of the first Miqo'te member of that line. I dunno. I just can't help but feel that its more complicated than our Miqo friend simply being a descendant. It pains him, but not the clones. Curious...