The genes (characters) in individuals then may be classified under two categories – these are (a) characters which do not show any difference in inheritance pattern in reciprocal classes and (b) characters which are inherited differently in reciprocal crosses. The characters of the first category are on the autosomes, while those of the second category are on the sex chromosomes. Such characters which are located on the sex chromosomes are called sex linked characters (sex linked genes) and the inheritance is called sex linked inheritance.