Maize is one of the most important cereal crops to be extensively characterized cytologically. McClintock (1929) gave the first indication of heterochromatinous knobs within pachytene maize chromosomes. Proceeding from chromosome morphology and data on the location of knobs, she provided early identification of all maize chromosomes. Later, other authors found that maize chromosomes carry as many as 29 knob-inducing regions (Longley 1939; Rhoades 1957; Rostovtseva 1967). Longley (1939) reported that knob location may serve as a marker to distinguish the lines.