Q20 - Comm and Robo Set Midline-Crossing Behaviour in Drosophila Neurons
In Drosophila embryos, developing neurons (red) grow along two columns parallel to the midline. Some traverse the midline and some do not, creating a ladder. Midline cells secrete a protein, called Slit, which is detected by the receptor, Robo. Comm, a transcription factor, controls Robo expression. To investigate how this guides neurons, WT (1), Robo knockout (2), Comm knockout (3), and Comm overexpression (4) flies were dissected.
Using the information and data, determine which of the statements are true or which are false.
A. Neurons cross the midline more often in Comm knockout flies, than WT flies.
B. Neurons are repelled when they detect Slit.
C. Comm acts to increase Robo expression.
D. Neurons increase Comm expression once they cross the midline.
Question reproduced from IBO 2017, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions