The Mutational Behavior of the R:Jana Allele in Zea Mays.

REVIOUS studies (STADLER and NUFFER 1953; STADLER and EMMERLING '1954) have shown that the action of the standard R' allele upon anthocyanin is due to two closely linked genes which are separable by crossing over. The identification of a sufficient number of crossovers within the R complex, together with evidence on the sequence of mutational steps, proved the existence of independent components. However, most of the experimental evidence on which this conclusion is founded is derived from studies with the allele R':Cornell. STADLER (1946), working with various R' alleles of diverse origin, found that spontaneous mutation usually affects seed color and plant color independently. But in none of the former studies had there been a check on crossing over. Consequently, it remains to be determined whether all R' alleles possess separable components. The most common type of mutational sequence observed by STADLER (1948) is illustrated in Figure 1. The R' alleles which mutate regularly to r' (seed color mutation) and R9 (plant color mutation) are Cornell, Boone, Quapaw, Ponca, and Black. Both common types of mutants, r+ and Rg, have given mutations to r9 (loss of seed color and plant color effect). In this group of R' alleles, mutations of R' to r g were rarely found, indicating that the action of the R segment is due to two separate genes rather than to the action of a single gene. However, this same investigation revealed that the stepwise course of spontaneous mutation shown by R': Cornell, Ponca, etc., is not characteristic of all R' alleles. ST.ADLER (1948) reported that two R' alleles with dilute pigmentation (R':Catspaw and Winnebago) mutate directly to 14 and not to r'. In the case of these two alleles, he concluded that both plant and seed color are dependent upon a single genetic component. The present report is concasned with a third type of R' allele which mutates regularly to r g and less frequently to r'. In contrast to R7:Catspaw and Winne-