Technically the House of Gwynedd is divided between the earlier House of Cunedda which lasted from c.420-825 — and the later House of Aberffraw beginning in 844.
The House of Aberffraw is believed by many to have become extinct on the death of Owain Lawgoch in 1378.
Under the laws of Hywel Dda, which were adapted from the much earlier pagan Molmutine Laws, any son can inherit from his father. This refers even to illegitimate sons if they are acknowledged by their father while he still lives. The throne cannot be inherited through the female line, unless her father was royal and so was the ancestry of her spouse. In many examples cousins were inter-married which made the distinction somewhat academic.
The House of Aberffraw began with the accession of Rhodri Mawr to the throne of Gwynedd. His father Merfyn Frych ap Gwriad had seized the throne of Gwynedd on the death of the last of the old royal line Hywel ap Rhodri Molwynog. He had married the former king's niece Ethyllt verch Cynan ap Rhodri Molwynog and their son, thus uniting both lines, was Rhodri Mawr.
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