II.5 Translocation T6-7aq.
D.R. Clark and R.T. Ramage Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721 USA. "R"
Seed of a homozygous translocation in the cultivar Betzes C.I. 6398 was given to us by R.F. Eslick and E.A. Hockett. The translocation, of spontaneous origin, was studied by Yu (Yu, Cheng-Wou. Chromosome behavior, breeding characteristics and seed set of partially sterile lines of barley, Hordeum vulgare L. M.S. Thesis, Montana State University, 1971). Yu reported 69.3 percent seed set in the heterozygous translocation. He also noted that the ring of four chromosomes of the translocation heterozygote was usually associated with the nucleolus and suggested that chromosome 6 was probably one of the chromosomes involved in the translocation.
We crossed the translocation onto a tester set to determine the chromosomes involved. The Fl's of crosses with Tl-3n, T2-4u and T3-5h all had two rings of four chromosomes indicating that chromosomes 1, 2, 3, 4, and 5 were not involved in Yu's translocation. The Fl's of crosses with T2-6s, T2-7m, T3-61 and T5-71 all had a ring of 6 chromosomes indicating that the translocation involves chromosomes 6 and 7. Fl's of crosses with T6-7t all had seven pairs of chromosomes, also indicating that Yu's translocation involves chromosomes 6 and 7. Therefore, this translocation has been designated T6-7aq.
Examination of chromosomes in root tips of T6-7aq indicated that the satellite of chromosome 6 was on a chromosome with a longer long arm, and the satellite of chromosome 7 was on a chromosome with a shorter long arm, than normal. Therefore, T6-7aq is probably broken in the short arms of both chromosomes or there has been an exchange of long arm segments of unequal length. Hauser and Fischbeck (as reported by Ramage, BGN 4: 111-113) stated that the break-points of T6-7t are in the same arms of both chromosomes but were unable to distinguish between Long-Long and Short-Short. Crosses of T6-7t with T6-7aq exhibit seven pairs of chromosomes at Metaphase I. This is expected if both translocations have their break-points in the same arms of both chromosomes.