One Gender Race: There are a few of these, most of them having got that way via their evolutionary process never having figured out sex, or natural hermaphroditism, or merely looking this way because of extreme sexual dimorphism; but also some exceptions – digisapiences, for example, have neither sex nor gender by default, although some of them adopt one. Many bioshells are manufactured in only one sex, usually neuter, and some clades – usually the made-to-an-ideal kind, likewise, without said usually.
But there are occasional weird exceptions. The shan kari, for example, are recovering from an approximation of this state (very slowly, because it did quite the psychological number on them, too), the anti-self-replication code in their robots having, through generalization, led to something of a Gendercide. Oops.