The development of new and better varieties of plants through plant breeding is essential to meet certain needs of a changing world. Genetics and a knowledge of its principles are the basis for such improvement. Barley has been used rather extensively in linkage relations studies. Its desirable characteristics are: (1) interspecific fertility and relative ease of hybridization, (2) numerous characters that are easily differentiated, (3) its commercial importance as a crop and (4) there are seven chromosome pairs in each of the four cultivated species.