Figure 17. . Sporidia (S) that have unlike alleles at the a and b loci are compatible. Under certain nutrient conditions they cease budding, begin secreting pheromones, and produce filaments that orient their growth toward the compatible partner. The mating filaments fuse and form a more vigorous dikaryotic infection filament (arrow). The right panel shows a fluorescent view in which nuclei are blue, microtubules are green, and chitin monomers are red, and probably are an indication of rapid elongation of the infection filament. (Courtesy K.M. Snetselaar) BACK