I understand there are three generations of quarks, which have the same charge but different mass. My question is, in a single generation how many different kinds of quarks are there. For example, in the first generation there are the up quark and down quark, each of which has an antiquark. So far, this is four different quarks in the first generation. Are there other properties in the first generation of quarks that would account for more first generation quarks? Thanks.