I always kinda thought as type being similar to fingerprints. It's something you're born with but it's not something you inherit from anybody. It just forms randomly. I certainly didn't inherit my personality from my parents - they're ESTJ and ESFJ and I'm INFP. There aren't even any other introverts in my entire family. But type is just supposed to explain your natural preferences, not your behavior. Your temperament is the part of your personality you're born with, but it's only half of the picture. Your full personality is the sum of your temperament and the effects of your environment and personal experiences, which is why there can be big differences even between people of the same type if they grew up in very different environments.
MBTI itself does not seem as if it would be genetic. And I don't agree with representing types purely as I/E, N/S, F/T, or J/P. Cognitive functions are much more reliable. You can have an ENTP and an INFJ parent and say that the child is more likely to be an N. But the fact of the matter is, ENTPs are dominant Ne and INFJs are dominant Ni so that intuition will not be the same.
If you stray away from defining types as a bunch of traits and behavioral characteristics and all that shit, what is it? It's a definition of how you think and how you look at things. That's what I think is genetic. Fi>Ne>Si>Te defines how you think and look at things, atleast, that's how I look at it. It makes sense that that's genetic or something you're born with.
Orbital, your theory has some promise. But this is an NP form, both recessive types. You'd need to ask Sensors and/or Judgers if their parents both have the recessive genes. For an example, an ESTJ couldn't be born to an INFP+INTP couple if one used your premise.
I think that dna would be a factor myself. I know this is circumstantial evidence (with a confirmation bias as well) but from my experience there are a number of INFP I have seen online who have SJ parents (mostly ISTJ or ESTJ) and these have the same cognitive functions as the INFP, only inverted in order (one of the weaker functions for one being one of the stronger for the other.) I'm tempted to say it may be occur in the meiosis stage with the sperm or egg, or perhaps the interaction of a sperm and an egg having different "types" would derail the results the bit, warping the type into another that. Other than that, it may change during development in the womb, due to stress/hormal conditions.
But all my theory is based off introspection alone and nothing else so believe it or humour it with a large pinch of salt, its your call.
There is a theory that says something that types have to do with DNA, so they are genetic.
I can't buy that theory. Because I can't see it in myself, but let's see what you guys say.
My father is an ISTJ (if so an ESTJ or an INTJ, but strongly Extroverted Thinking) and my mother is an ISFJ. Well, my mother can look like an ISFP many times, but she's not INFP or INTP.
And then I appear. I can see how hard our relationship is, and I think it has to do a bit with types.