Beyond This Horizon
, an early Heinlein novel, describes a technology for what I like to describe as libertarian eugenics, a way in which a couple can choose, among the children they could have, which one they do have. The central trick is a way of separately analyzing the genes of sperm and egg before combining them.
The obvious problem is how to analyze a cell without damaging it. Heinlein's ingenious solution takes advantage of the fact that egg and sperm each contain half of the full set of genes of the cell from which it is derived—and the process that produces an egg or sperm also produces other bodies with the rest of genes. Analyse an ordinary cell, analyse the extra body, subtract, and you now know what genes are in egg or sperm.
According to a news story
published yesterday, someone is finally attempting a version of Heinlein's idea, looking at the polar body
that contains the genes that are not in the egg in order to deduce the genes that are. At least, that is what the story seems to be describing, although there are not enough to details to be certain.
Heinlein published the novel, and the idea, in 1942.