On the Genographic website, R1b is associated with M343. The following is found in the text describing R1b/M343:

"The lineage is essentially defined by M173-carrying individuals who never acquired an additional marker, such as M17."

What do they mean when they say that M343 does not have an additional marker from M173? I thought that both R1a and R1b had an additional marker from R1/M173 (M17 for R1a, M343 or P25 for R1b).