King Pariksit married the daughter of King Uttara (Iravati) and begot four sons, headed by Maharaja Janamejaya

Expressions researched:
"King Pariksit married the daughter of King Uttara and begot four sons, headed by Maharaja Janamejaya" |"in the womb of Iravati, Maharaja Pariksit begotten four sons. The first one's name is Janamejaya"

SB Canto 1

King Parīkṣit married the daughter of King Uttara and begot four sons, headed by Mahārāja Janamejaya.

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.

Janamejaya: One of the rājarṣi kings and the famous son of Mahārāja Parīkṣit. His mother's name was Irāvatī, or according to some, Mādravatī. Mahārāja Janamejaya begot two sons of the names Jñātānīka and Śaṅkukarṇa. He celebrated several sacrifices in the Kurukṣetra pilgrimage site, and he had three younger brothers named Śrutasena, Ugrasena and Bhīmasena II. He invaded Takṣaśilā (Ajanta), and he decided to avenge the unlawful curse upon his great father, Mahārāja Parīkṣit. He performed a great sacrifice called Sarpa-yajña, to kill the race of serpents, including the takṣaka, which had bitten his father to death. On request from many influential demigods and sages, he had to change his decision to kill the race of snakes, but despite stopping the sacrifice, he satisfied everyone concerned in the sacrifice by rewarding them properly. In the ceremony, Mahāmuni Vyāsadeva also was present, and he personally narrated the history of the Battle of Kurukṣetra before the King. Later on by the order of Vyāsadeva, his disciple Vaiśampāyana narrated before the King the subject matter of Mahābhārata. He was much affected by his great father's untimely death and was very anxious to see him again, and he expressed his desire before the great sage Vyāsadeva. Vyāsadeva also fulfilled his desire. His father was present before him, and he worshiped both his father and Vyāsadeva with great respect and pomp. Being fully satisfied, he most munificently gave charities to the brāhmaṇas present at the sacrifice.

Srimad-Bhagavatam Lectures

In the womb of Irāvatī, Mahārāja Parīkṣit begotten four sons. The first one's name is Janamejaya.

Lecture on SB 1.16.2 -- Los Angeles, December 30, 1973:

So here Mahārāja Parīkṣit, son of Uttarā, but he married his maternal uncle's daughter. That was permissible. Still it is permissible. This kind of marriage is considered very aristocratic, to marry the daughter of maternal uncle. So Arjuna also married the daughter of maternal uncle. Kuntī is the sister of Vasudeva, Kṛṣṇa's father, and Subhadrā is the daughter of Vasudeva. So he also married. Except in Southern India, this process is now no longer existing. In Bengal and other provinces of India, they do not marry the first cousin. So that is the marriage system. But in southern India, still, to marry the daughter of maternal uncle is considered as very aristocratic. So this system was current five thousand years ago also. So Mahārāja Parīkṣit married his uncle's daughter, uttarasya tanayām. Tanayā means daughter. Uttarasya tanayām upayema. And her name was Irāvatī, Irāvatī.

So in that, in the womb of Irāvatī, Mahārāja Parīkṣit begotten four sons. The first one's name is Janamejaya. Ādi. Ādi means "beginning with." He begotten four sons, beginning with Janamejaya. The history of Janamejaya is also very nice. (aside:) You can read the Janamejaya paragraph.