Gotra
Srimad-Bhagavatam
SB Canto 1
SB 1.16.2, Translation and Purport:
King Parīkṣit married the daughter of King Uttara and begot four sons, headed by Mahārāja Janamejaya.
Mahārāja Uttara was the son of Virāṭa and maternal uncle of Mahārāja Parīkṣit. Irāvatī, being the daughter of Mahārāja Uttara, was the cousin-sister of Mahārāja Parīkṣit, but cousin-brothers and -sisters were allowed to get married if they did not belong to the same gotra, or family. In the Vedic system of marriage, the importance of the gotra, or family, was stressed. Arjuna also married Subhadrā, although she was his maternal cousin-sister.