After reading the paragraphs below, answer the questions that follow.
Oligodendrocytes are cells in the brain that produce myelin in the central nervous system. Myelin regulatory factor (MyRF) is a transcription factor that is required by oligodendrocytes in order to produce myelin. Researchers investigated the importance of MyRF by having mice learn how to run on complex wheels (there were many gaps in the wheel thus making it difficult to run on—see graph below).

Researchers created a genetic strain of mice that were lacking both genes for MyRF. What is the most likely effect that this would have on the mice?
◦ increased flow of ions through voltage-gated sodium channels
◦ decreased flow of ions through voltage-gated potassium channels
◦ increased number of dendrites on neuron cell bodies
◦ decreased rate of signal propagation via axons