Do they exsist? never seen them in the games I know Breton are from mixing with elves, but thats not really a half elf.

When members of two different races breed, the child will essentially be of the mothers race, with a smidge of traits from the father. So your either gonna get an elf or a human, but not a half elf, when an elf and a human have a baby.

Aw ok that sort of makes sense now how Breton came about if they mixed with elves, but vastly outnumbered them. Why Mother tho was that ever explained? A genome is a genome.

"with a smidge of traits from the father"

This was done over hundreds of years. The small pieces of father heritage mounted up over the years. I would assume they are predominantly human, and they don't actually have all that much Mer in them. They are only more magical. They don't seem to have all that much physical resemblance to Mer.

And it's your fault for assuming that RL Biology applies just the same.

http://www.imperial-library.info/content/morrowind-notes-racial-phylogeny-and-biology, the in-game book that explains breeding, and the dev's in-character way of saying "we're not doing half races."