Linkage between translocations and row‑number genes.

As part of an extensive study on the inheritance of kernel-row number in maize, the late Dr. R. A. Emerson was interested in obtaining experimental evidence on the number and location of genes affecting the expression of this quantitative character. In tests similar to those of Lindstrom (Iowa Agr. Exp. Sta. Bul. 142. 1931). Doctor Emerson collected considerable data on apparent linkages between genes for kernel‑row number and known marker genes. He concluded from his results, however, that some (if not all) of the associations observed were due to the effects of the "qualitative" genes themselves on row number.

In order to avoid this false evidence of linkage, a study similar to those of Burnham and Cartledge (1939) and Saboe and Hayes (1941) was planned. In this method chromosomal interchanges serve as genetic markers and plants heterozygous for a translocation show no apparent difference from normal other than reduced fertility. The semisterility, caused by abortion of approximately 50% of both ovules and pollen, is used as a "dominant" marker in backcross tests.

According to the records available Dr. E. G. Anderson and Dr. C. R. Burnham supplied Doctor Emerson with 36 different interchanges so chosen that each of the chromosomes was reasonably well represented. The locations of the points of breakage have been determined by Doctors Anderson and Burnham as shown in their published and unpublished data.

The interchanges were crossed repeatedly to a series of different 8‑rowed lines in order to obtain, without loss of vigor, heterozygous interchanges in lines with 8‑kernel rows on the ear. By the summer of 1947, 35 of the interchanges were present in a heterozygous condition in vigorous 8‑rowed lines and at that time four 12‑rowed inbreds were crossed to each of these lines. Although there was a tendency for the F₁ plants heterozygous for the interchanges to have a slightly lower mean number of rows than their normal sibs, the differences were not significant at the 1% level of probability.

This year the backcross progeny will be grown and the plants classified for row number and semisterility. The data will be analyzed for evidence of linkages between genes for lower row number and semisterility or higher row number and fertility.

T. J. Mann