Genetic male sterility has been used in barley breeding and research since its discovery in 1940. It has been used as genetic emasculation in simple crosses, to create large composite cross populations (CC), in male sterile facilitated recurrent selection (MSFRSP), and in the systematic introgression of desired traits into adapted backgrounds (RIPE system). The use of genetic male sterility is enhanced by linkage to easily distinguished phenotypic marker genes. A highly efficient system of pre-sowing selection of male sterile plants was developed by combining the xenia-expressing shrunken endosperm gene sex1 with the male sterile gene msg6 near the centromere of chromosome 6. The stock used also included the orange lemma gene rob which is located between sex1 and msg6. This gene block (sex1-rob-msg6) is being used to increase crossing efficiency in several programs around the world. A further modification of the system is the removal of the rob allele from the sex1-msg6 gene block and the use of it in repulsion with the male sterile. Thus, in segregating populations (ie. F2), shrunken seed would produce male sterile plants with normal lemma pigmentation (sex1-Rob-msg6/sex1-Rob-msg6), plump seed which produced fertile plants with normal lemmas would be heterozygotes for the gene block (sex1-Rob-msg6/Sex1-rob-Msg6), and fertile plants with orange lemmas would be homozygous for plump seed and normal fertility (Sex1-rob-Msg6/Sex1-rob-Msg6). All orange lemma plants could proceed directly into a normal evaluation process without progeny testing for male sterility. The heterozygotes could be used as a source of more male sterile plants (from shrunken seed) for further crossing. All resulting cultivars would have the orange lemma gene.