[Peptobismol]

it is believed that every person originates/progenates from one Rishi resulting the offsprings become brothers/sisters. as we know, brothers and sisters dont marry. That is it prohibits marriage between same gotra persons. As Dr Renuka infer, even marriage between cousins is not advisable but we do viz. marriage between offsprings of sister and brother, of uncle and aunt etc. personally if you ask me, I dont advise marriage beween same gotras. but I know some such marriages