A key plot point in Game of Thrones is children's inherited physical characteristics from their parents. How was heredity understood in medieval Europe?

by crrpit

I've tried to keep the wording vague to avoid spoilers (if that's even possible at this point) , but I'm referring to>! a main character's realisation in Book/Season 1 that King Robert's blonde children aren't his own, because his family always produces children with black hair.!<

I can only assume that people noticed in real life that children inherited characteristics from their parents - how did they understand or rationalise this?

SuicideRabbit

Follow up/ side question:

There were in some European courts (especially the Habsburg court in 16th century) genealogists who worked to prove lineages of their respective rulers to, usually far sought, historical figures such as romans. Did these genealogists also do actual research into the appearances of family trees and physical traits, or did they just try to make up a story with false documents and speculation?