I think I heard in high school science that there is something like 16,000 possible gene combinations with any 2 parents. That means you could, in theory, have 16,000 children without ever having 2 the same, barring identical twins. My husband and I have 5 children. He and I are both brown-haired and so is just about everyone in both our known families. Our second son had white blond hair among 4 brunets. It must have come from somewhere back in the family tree ... and not the mail man as many people have suggested! You should see my 5 foot 6 husband standing beside our middle son who is 6 foot 2. My father and brother are that height, but it looks odd to see my husband and son together.
I would also add that anyone getting DNA testing done should be prepared for surprises. Our known ancestry from oral tradition and paper documents is not always ironclad proof of anything. My father does family tree research with another man of the same family line and surname. A few years ago, Dad, that man and some cousins of the man all did Y DNA together. Everybody got the close DNA matches they were expecting except the research partner who was not even in the ballpark! Apparently, somewhere in the last 100 years, there was what I call a paternity event. It could be as simple as an adoption which were not regulated, documented or even ever mentioned to the child in question. It could be an extramarital affair. It could be a baby of an unwed girl raised by her parents as her sibling. His expected Scottish roots turned out to be more Germanic in origin. I may get a surprise too! I will have to wait and see now.