2020-12-21 19:41 HIV-1 is the most common and pathogenic strain of the virus. Scientists divide HIV-1 into a major group (Group M) and two or more minor groups, namely Group N, O and possibly a group P. Each group is believed to represent an independent transmission of SIV into humans (but subtypes within a group are not). A total of 39 ORFs are found in all six possible reading frames (RFs) of HIV-1 complete genome sequence, but only a few of them are functional.