I'm fairly new to quantum mechanics, and I was looking up some basic information about the weak force and it's interactions. I found this equation of weak hypercharge on Wikipedia and quoted a few other places.
Hypercharge = $Y = B + S + C + B′ + T$
B is the Baryon number which is always 1/3 for quarks.
S = strangeness which is a function of the number of strange and anti-strange quarks.
C = charm which is a function of the number of charm and anti-charm quarks.
B' = bottomness which is a function of the number of bottom and anti-bottom quarks.
T = topness which, as you might expect, is a function of the number of top and anti-top quarks.
For me, noticeably absent are the $up$ and $down$ quarks. If the Baryon number is always $1/3$ for quarks no information about the type of quark should influence it (I think). I suppose that if I were to describe the hypercharge of an $up$ or $down$ quark, I might set all parameters except B to zero; in which case the Hypercharge would be $1/3$. However, this would mean that the $up$ and $down$ quarks have different hypercharges from all the other quarks. Which intuitively seems strange. Why isn't hypercharge a function of "up-ness" and "down-ness" in addition to all the other parameters?