heterozygotic

It arises in one individual but spreads in population in heterozygotic form, untill in becomes frequent enough to produce homozygotic mutants people who inherited it from both parents.

Just call him/her Ol’ Blue Eyes 2010

The second has a couple of good paragraphs on how heterozygotic copies of bad genes can confer evolutionary advantages I told you I was going somewhere with this.

"Sicker than a Doorknob" 2007

That's about 450 is the US units. 600 has been recorded (rarely) amongst people with the heterozygotic (1 copy) form of the mutation, and nearly double that for homozygotes (2 copies).

Archive 2005-05-01 Zoe Brain 2005

That's about 450 is the US units. 600 has been recorded (rarely) amongst people with the heterozygotic (1 copy) form of the mutation, and nearly double that for homozygotes (2 copies).

Things You Don't Want To Hear Your Doctor Say Zoe Brain 2005

I would posit that the low-lifespan-after-senescence-onset would likely have a similar effect -- heterozygotic organisms (and maybe the homozygotes too) may have an advantage in terms of metabolism or ability to reproduce or something.

Boing Boing 2009

There are many instances recorded in Earth history of apparent telepathic links between monozygotic twins, but fewer of such links between heterozygotic twins, who are born together but are genetically different. "

Spock Must Die Blish, James 1970