is generally not functional, since it lacks the promoter
at the beginning, or since it is inserted in a region of the genome
which is not transcribe
d. This is still "useful" in evolution
ary terms, since it might be reactivated after some mutation
s occur. This (both with and without reactivation) is the evolutionary cause of homologous gene
Some pseudogenes are, however, completely "useless" in this sense -- see processed pseudogene.