Yeast Gradient Tracking
Yeast can track mating pheromone and grow towards its source. Here, yeast are experiencing a gradient coming from the right.
At the far right of the gradient, the dose of pheromone is so high that the yeast form Shmoos, tight mating projections that will fuse with other yeast if they contact them.
In the middle of the gradient, the yeast experience an intermediate dose of pheromone, and elongate towards its source. This is where yeast undergo chemotropic growth, otherwise known as gradient tracking.
At the far left of the gradient, the pheromone dose is so small that the yeast do not respond to it, and instead continue through the cell cycle, budding off daughter yeast.