Breeding nutritional Neanderwheat

On the topic of introgression, this article by Reuters' Will Dunham is a good illustration:

A team led by University of California at Davis researcher Jorge Dubcovsky identified a gene in wild wheat that raises the grain's nutritional content. The gene became nonfunctional for unknown reasons during humankind's domestication of wheat.
Writing in the journal Science on Thursday, the researchers said they used conventional breeding methods to bring the gene into cultivated wheat varieties, enhancing the protein, zinc and iron value in the grain. The wild plant involved is known as wild emmer wheat, an ancestor of some cultivated wheat.

Introgression between domesticated crops and their wild relatives is one of the most common ways to introduce desirable traits into agricultural production. For the most part -- even when they are classified as different species -- domesticated crops can be crossed with wild progenitors.

Emmer wheat is itself a tetraploid, presumed to be a hybrid of two wild diploid grasses. Tetraploidy (and other -ploidies) come to mind when talking about plant hybrids, because it often happens that new plant species originate from such crosses. There's nothing so exotic about emmer-domesticated wheat introgression, since wheat is also tetraploid. The ability to breed in characteristics is simple Mendelism:

"We didn't do it by genetic modification. The normal wheat crosses perfectly well with the wild wheat. So we just crossed it after normal breeding," Dubcovsky said.

Breeders can take the selection coefficient all the way up to 100 percent if they want, and so ensure the fixation of a desirable allele like this one. Natural popluations usually don't have this privilege -- and advantageous alleles are often lost, despite being favored by selection. A process carried out methodically by breeders reduces to a scattershot in nature. But it is an orderly scattershot in one way: the most strongly selected alleles have the highest chance of making it.