1) Ingress 
Introgression, also known as introgressive hybridization, in genetics (particularly plant genetics) is the movement of a gene (gene flow) from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Purposeful introgression is a long-term process; it may take many hybrid gen...
• (n.) The act of going in; entrance.
Backcrossing of hybrids of two plant populations to introduce new genes into a wild population.
Backcrossing of hybrids of twoplant populations to introduce new genesinto a wild population. ... (09 Oct 1997) ... 
Introduction of genes from one population or species into another.
The entry or introduction of a gene from one gene complex into another.
In`tro·gres'sion noun [ Latin introgressus , past participle of introgredi to go in; intro- within + gradi to step, go.] The act of going in; entrance. Blount. 
The movement of genes from one population into another through hybridization followed by backcrossing. Usually refers to movement of genes from one species to another or among sub-species that have been geographically isolated then brought back together by changes in the species ranges or planting of exotic populations. (See gene flow.) 
the introduction of genes from one species into the gene pool of another species, occurring when matings between the two produce fertile hybrids. Also called