Complex sentence: Allerton Jr. was born in Plymouth, Massachusetts, the son of Mayflower Pilgrim Isaac Allerton and his wife Fear Brewster his mother died either in 1633 or 1644 he was the maternal grandson of mayflower pilgrim Elder William Brewster and Mary Brewster.
Split into simpler sentences: Allerton Jr. was born in Plymouth, Massachusetts, the son of Mayflower Pilgrim Isaac Allerton and his wife Fear Brewster. He was the maternal grandson of Mayflower pilgrim Elder William Brewster and Mary Brewster.