I just found out last night that my mum is a (well balanced) ENTP. It was a close call, but the best bet.
She is a definitive P, cheared when I read her Keirsey´s description of a NT childhood ("so me!") and stopped me almost immerdiately when I read her the INTP portrait ("oh god, no!") and identified most with the ENTP description (minus the daredevil part). She grew up closer to my grandfather than to my grandmother as the youngest of four with two brothers and a sister. As a university student in the early seventies they once did a computerized test that would evaluate your answers to certain psychological questions and then tell you your gender. She came out male and is pissed till this day about the questions´ sexist bias. As a science teacher she fits Keirsey´s description of NT teaching style to a T (ha ha, see what I did there?!).
Part of the reason my parents got divorced when I was 6 years old was that my dad (not typed yet, a general practitioner turned pysochoanalyst, says he loves math and science but is also very emotional and soft and uses extremely fuzzy logic at times) thought that she wasn´t soft and feminine enough for his taste. Oh, and when I told her that her constantly teasing us kids and her sarcasm fit right she denied it for a second and then started smirking at her own fruitless attempt to deny it.
I was raised by my mum together with a younger sister and brother. They both went into science (I´m the only one in humanities, mum always insisted that 1. there is nothing masculine about math and science and 2. you can love and be good at science and humanities at the same time, she hates being nailed down to only one side and has well developed S and F even though she has an overall preference for NT). I´m not sure about my brothers type (big time nerd in some respects, but also a lot of SP in him), my sister is a self-tested ISFP who is a math crack with a PhD in molecular biotechnology. They both love hands-on science: working in the lab (her) or taking algae samples for further analysis (him, currently in Sumatra!!!)
So how much of this is genetics and how much is environment?
PS: This finally helped me understand how she can appear a bit emotionally removed a times while loving us very much. I never gave it much thought, but knowing she´s an NT explains a lot about our childhood (she highly values independence, is very loving but not really the sweet touchy-feely type, etc.) as well as my parent´s failed marriage.