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 the Appendix of Indo-European roots.]
in′tro·gressive (-grĕsĭv) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.