IV. 11. Coordinators Report: Translocations and balanced tertiary trisomics.
R. T. Ramage and C. L. Crandall, Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, U.S.A.
No new translocations have been added to the collection since 1976. Ramage and Scoles (BGN 11: ) report the establishment of five balanced tertiary trisomics that have an extra T27d chromosome and two normal chromosomes carrying recessive seedling lethal alleles and probably the recessive male sterile allele msg2. The seedling lethal alleles in these BTT's are albino-58, xantha-116, xantha-415, albino-530, and albino-737. These five BTT's have been added to the World Collection.
We are continuing the project designed to confirm or assign breakpoints to arms in the World Collection of Translocations by the intercross method. We are concentrating on those translocations between chromosomes 1, 2, 3 and 4, i.e., T1-2, T1-3, T1-4, T2-3, T2-4 and T3-4 translocations. Identification of break-points in translocations between these four chromosomes by cytological observations alone is difficult because of the similarity in length and arm ratios. Observation of Metaphase I of intercrosses between translocations can be used to assign break-points to either the same arm in one chromosome and in opposite arms in the other chromosome or to the same arms in both chromosomes or opposite arms in both chromosomes. Pollen and ovule abortion can sometimes be used to separate those intercrosses that are broken in the same arms of both chromosomes from those that are broken in opposite arms of both chromosomes. Appropriate linkage tests can be used to distinguish those intercrosses that can not be assigned to class by pollen or ovule abortion.
We are experiencing some difficulties in distinguishing intercrosses between translocations broken in the same arms of both chromosomes from those broken in opposite arms of both chromosomes. Both classes of intercrosses are expected to exhibit seven pairs of chromosomes at Metaphase I. Opposite-arms intercrosses are expected to have about 50% pollen and ovule abortion while same-arms intercrosses are expected to have from O to 50% abortion, depending upon the similarity of break positions in the two translocations. The majority of the intercrosses that we have looked at have had between 35 and 50% abortion. Very few of the intercrosses have shown less than 20% abortion. It could be that most of the intercrosses that we have looked at are opposite-arms intercrosses with an expected 50% abortion; however, we see no reason why the two types of intercrosses shouldn't be equally frequent. One explanation for the observed large number of intercrosses with close to 50% abortion is that barley can not tolerate even small amounts of duplication-deficiency for chromosome 1, 2, 3 and 4.
Limited amounts of seed of the translocations and balanced tertiary trisomics in the World Collection are available upon request.
BGN 11 toc
BGN Main Index