Two types of chevrons have been found in the conduction regime, as well as the conventional chevrons in the dielectric regime in homeotropically-aligned nematics. These two are named the defect-mediated chevron (DMC) and the defect-free chevron (DFC) by their structure changes. Two different bifurcation sequences are found with increasing the applied voltage, such as Freedericksz transition --> normal rolls --> abnormal rolls --> defect chaos --> DMC for low frequencies and Freedericksz transition --> prewavy pattern --> DFC for high frequencies. Moreover, the double periodicity of the chevrons (i.e., the short wavelength lambda (1) of the striated rolls and the long wavelength lambda (2) of the chevron bands) shows quite specific frequency dependence.