Chromosomal Interchanges in Barley

Thirty-four chromosomal interchanges are reported, the result of X-raying of seeds of barley. One line had two separate rings of four chromosomes each.Pollen abortion in plants with one ring ranged in different lines from 14 to 58 per cent, the average being 28.8. The search for a line with rings but no pollen abortion was unsuccessful, however, the number of lines ex-amined was not large.Stocks homozygous for the interchange have been established for 28 of the 34 lines. The use of a tester set of five interchanges in identifying the chromosomes involved in new interchanges is illustrated. The chromosomes have been labeled temporarily by the letters a through g. The testers are a-b, b-d, c-e, e-f, and c-d, the last being needed to identify only certain combinations.Trisomics have been identified in the progeny of plants heterozygous for an interchange, the configuration at meiosis being a chain of 5 chromosomes.The g chromosome carries the large satellite, confirming the result of Hagberg and Tjio.Linkage tests with different interchanges involving only one chromosome in common indicate that the e chromosome carries linkage group IV, f carries group V. b carries group III.Their usefulness in supplementing the genetic linkage markers in tests to locate new genes is illustrated.They will make it possible to test and establish the independence of the 7 linkage groups; to identify each linkage group with its chromosome. Studies which are in progress to determine the breakage points in the chromosomes and in the linkage groups will make them usable for special problems.

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