IIa precursor is transformed into a IIb precursor.
Homozygotes have more sensory neurons than normal.
Overproduction of sensory neurons. Defects in the embryonic PNS, number of es and cho neurons is approximately doubled due to transformation of the outer support cell and cap cell respectively. Mosaic analysis demonstrates loss of ttk function in the adult leads to the appearance of supernumerary neurons at the expense of hair and socket cells.