II. 36. Proposed method for accumulating genes for alternate segregation from a large ring.
S. L. Morgan and R. T. Ramage. Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, U.S.A. "R"
Efforts to accumulate genes for alternate segregation in a translocation heterozygote in barley are now in progress. Several complete interchange stocks are available (BGN 3:84-86) and one of them is being used for this purpose. The complete interchange stock involves all seven chromosomes in a series of translocations. When this stock is crossed with a line with normal chromosomes, a large ring containing fourteen chromosomes is observed at metaphase I in the F1. The only viable gametes produced by such an F1 would either be those containing the centromere segments of the seven normal chromosomes or those containing the centromere segments of the seven interchanged chromosomes. All other gametes would contain duplication deficiencies and would be expected to abort. The two types of viable gametes could only be produced by complete alternate segregation of the ring of fourteen chromosomes during meiosis.
During the spring of 1976, the complete interchange stock was crossed onto 450 male sterile plants. Approximately 19,000 crossed seed were obtained. The Fl's were grown in Montana during the summer of 1976. The F2 is currently being grown in Arizona.
Cytological material from the F1 and F2 plants has been collected. Meiosis is being studied in this material. The areas of interest are the metaphase configurations, numerical segregation of chromosomes at anaphase, and the percentage of aborted pollen. These observations should give an indication of meiotic behavior expected from a complete heterozygous interchange.
The F2 should contain only three types of plants since only two types of viable gametes are expected from the F1. The three types of plants should include male sterile plants with all normal chromosomes, plants heterozygous for a ring of fourteen chromosomes which are highly sterile, and male fertile plants that are homozygous for the complete interchange. Since all of these plants resulted from the union of gametes which arose as the result of alternate segregation, genes for alternate segregation should be present in these plants. Crosses are now being made between the male sterile and male fertile plants in the F2 population. These crosses should be between male fertile plants homozygous for the complete interchange and male sterile plants homozygous for the normal chromosomes. The F1 will be grown and in the F2, crosses between male sterile and male fertile plants will again be made. This type of intercrossing will be continued in future generations in an attempt to accumulate genes for alternate segregation.