or·tho·log or or·tho·logue 
(ôrthə-lôg′, -lŏg′)
(ôrthə-lôg′, -lŏg′)n.
A homologous gene that is related to those in different organisms by descent from the DNA of a common ancestor and that may or may not have the same function.
[Back-formation from orthologous : ORTHO- + (HOMO)LOGOUS.]
or·tholo·gous (-thŏlə-gəs) adj.