One thing to note is that up and down quarks are separated by exactly one unit of charge (2/3 is 1 more than -1/3). The charge coincidence is one of the reason

One thing to note is that up and down quarks are separated by exactly one unit of charge (2/3 is 1 more than -1/3). The charge coincidence is one of the reasons that scientists are looking for a grand unified theory -- part of which would ultimately mean that in some sense quarks and electrons are _the same thing_, and the electroweak and strong forces would be unified.