Genetic mechanisms determining the central visual pathways of mice.

Albino mammals have abnormal visual pathways. "Flecked" mice have a variegated pigment distribution, with roughly half the cells normally pigmented and half albino. They do not show the albino abnormality in the visual pathways. The gene at the albino locus, which determines the course of the visual pathways must, thus, have an extracellular action.