Direct Gene Flow: occurs via mating
Indirect Gene Flow: occurs via an intermediate population (X mates with Y. Y mates with Z. There is gene flow between X and Z via Y)
The biological species concept defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. This means that all members of these populations can contribute to a common gene pool. These populations belong to the same species. Genes are transferred between these populations through both direct and indirect gene flow.
Biologists studying disease susceptibility in mice used genetic techniques to look for gene flow in 12 wild populations of mice. The populations (designated A through L) were located along a 210-km transect line.
The researchers found evidence of gene flow between some, but not all, pairs of populations. In the grid below, a "+" indicates a pair of populations in which direct gene flow was detected, and a "–" indicates a pair that showed no evidence of direct gene flow.
The researchers discovered that the 12 populations could be organized into 3 distinct species. Populations A, B, and C each belong to a different species. Use the data in the grid to sort each population to the species to which it belongs. D, E, F, G, H, I, J, K, L.