Motility pattern with two turning events.

<p>During each run, the speed of the cell <i>v</i>₀ is constant. Motion is nearly straight and is affected by the rotational diffusion <i>D</i>_<i>r</i>. The cell changes the direction of its motion during turning events (black dots), where turning angles Δ<i>φ</i>_1,2 are allowed to have two different probability distributions. Importantly, the cell strictly alternates the two types of turning events. When swimming in the gradient of signaling chemicals ∇<i>c</i>, the cell can bias its motion and respond with a drift speed <i>v</i>_<i>d</i> in the direction of the gradient, which we want to calculate.