I think it's maybelline.
I don't know if it's hereditary, but to a certain extent it's probably fixed (ie, I'll be ENFP for the rest of my life). Also, P and E aren't traits/functions in themselves. P means your perception function (N or S) is extroverted. E means your dominant function (N, S, T, or F) is extroverted.
Btw, according to Myers Briggs theory, there are 8 cognitive functions:
Introverted Sensing, extroverted sensing,
introverted and extroverted intuition,
introverted and extroverted thinking,
introverted and extroverted feeling.
The four letter code indicates which functions one has and what order they're in (dominant, auxiliary, tertiary, inferior). The P/J in particular was invented by MyersBriggs for this purpose. Check it out:
Understanding the Eight Jungian Cognitive Processes / Eight Functions Attitudes