What is the difference between genetic introgression and genetic admixture ? Are these terms interchangeable ? Do they apply to different population scopes or something ? The usage seems kind of vague to me. Looking for some clarification.
The difference is referring to the directionality of gene flow.
We talk about genetic introgression when there is some gene flow from one population (say, population A) to the other (say, population B). We would say that population A introgresses into population B. If gene flow goes both ways, then the two populations A and B are admixing.
Introgression, also known as introgressive hybridization, in 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.
Genetic admixture occurs when two or more previously isolated and genetically differentiated populations begin interbreeding.