Y chromosomes and mitochondria don't have crossover, so you need unbroken patrilineal and matrilineal descent from a particular ancestor to inherit it. So if y

Y chromosomes and mitochondria don't have crossover, so you need unbroken patrilineal and matrilineal descent from a particular ancestor to inherit it. So if you are Ugg, son of Ugg, son of Ugg, son of Ugg, you have ur-Ugg's Neanderthal Y chromosome, but if you are Ugg, son of Ugg, son of Uggette, daughter of Ugg, you have neither ur-Ugg's Y nor X chromosome (Uggette inherits Ugg's X, which gets crossed over with Maggie's [Ugg's Cro-Magnon missus] X's and passed on to Ugg II, but Ugg II doesn't pass on his X to you, he passed on Magnus's [Uggette's Cro-Magnon mister] Y).