/in'treuh gresh"euhn/ , n. Genetics.
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 introgressive hybridization /in'treuh gres"iv/ .
[ 1930-35 (earlier in literal sense of L); introgress ( us ), ptp. of introgredi to go in, enter ( intro- INTRO- + -gred-, comb. form of grad ( i ) to proceed, walk + -tus ptp. suffix, with -dt- > -ss- ) + -ION ]