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The movement or spread of alleles of one species into the gene pool of another through repeated backcrossing of interspecific hybrids with members of one of the parental species.
[From Latin intrōgressus, past participle of intrōgredī, to step in : intrō-, intro- + gradī, to step; see ghredh- in Indo-European roots.]
in′tro·gres′sive (-grĕs′ĭv) adj.
(Genetics) the introduction of genes from the gene pool of one species into that of another during hybridization