Panini defines gotra for grammatical purposes as apatyam pautraprabhrti gotram (IV. 1. 162), which means ”the word gotra denotes the progeny (of a sage) beginning with the son’s son.” When a person says ”I am Angirasa-gotra”, he means that he traces his descent from the ancient sage Angirasa by unbroken male descent.

All members of a particular gotra are believed to possess certain common characteristics by way of nature or profession. Many theories have been propounded to explain this system. According to the Vedic theories, the Brahmins are direct descendants of seven sages who are believed to be the sons of Brahma, borne out of his mind through yogic prowess. They are

(1) Gautama (2) Bharadwaja, (3) Vishvamitra, (4) Jamadagni, (5) Vashista, (6) Kashyapa and (7) Atri .
To this list, Agastya is also sometimes added. These eight sages are called gotrakarins, from whom all 49 gotras (especially of the Brahmins) have evolved. For instance, from Atri sprang the Atreya and Gavisthiras gotras.

Marrying the same Gotra means marrying your sister/brother, with the same sets of genes. There are some research that claims that the third-generation kids of such couples suffer genetic disorders.

The Gotra system had a significant contribution in preventing genetic abnormalities since its inception thousands of years ago. If the child to same parent or close relative is married, then recessive gene may accumulate and express themselves for its harmful effect (e.g. Haemophilia)

However, there is no harm in Sagotra marriage, if the individuals are not related to six generations both from the maternal and paternal side, as brought out in chapter 5 of Manu smriti at mantra 60, which states that sapinda ends after seventh generations.