Table 2.

Distribution of olfactory receptor genes in families and subfamilies

	Number of classes	Number of families	Number of subfamilies
Human*	2	17	300
Mouse†	2	Nd	241
Dog	2	23‡	300
Rat	2	21	282

*From [32]. ^†From [19]. ^‡Note that this number of families is lower than that previously published [21]. This is probably because the published number was calculated from the alignment of the middle part of the sequences, which is more diverse, particularly for transmembrane domains TMIII and TMIV. Nd, not determined.