Gothra and´ Chromosome
Gothra is no more than the Rishi, whose home university one studied in. Even to-day we identify people as alumni of a particular university or school, and they claim many traditions etc. in common. So is Gothra. Many of the Rishis, Moudgalya for instance were not brahmins. Gowthma's wife, Ahalya is said to have had an affair. So, extending gothra concept to geneology would be asking for trouble. For the same reason, it is illogical not to be married into Sagothra families. I am a strong votary of this. In any case, just ponder and ask how common or different we are to the Rishis of old who lent their names to these incongrous groups.