2. Mutation of a to different alleles.
Four alleles at the a locus have been described by Emerson and Anderson. These four are a, ap, A and Ab. Only a has its mutation rate increased by Dt. Mutation of a to five different alleles has occurred in a Dt stocks. One of the five is a mutation to an allele similar to a in its effect on aleurone, plant and pericarp color but differs in that it is stable with Dt. This allele has been found several times. It is of some interest that these so-called stable alleles are not completely stable with Dt; an occasional dot is found in the aleurone (about .4 dot per seed in Dt Dt Dt seed) but these dots are commonly much smaller than normally is the case indicating that the mutations when they do occur take place at a relatively late stage.
A second allele is one identical in all respects with A. Out of twenty mutations tested, which give deep aleurone color and purple plant color with B Pl, eighteen of them were to A.
A third allele was found in the group of twenty mutations mentioned above. This allele produces deep aleurone and purple plant color but gives a recessive brown pericarp color with P. This is a new allele.
A fourth allele is one like A in its effect on aleurone and plant color but produces a red-brown pericarp color that is recessive to the red color produced by A but is dominant to the recessive brown of a. This is a new, previously undescribed allele.
The fifth allele found is one resembling ap in its effect on aleurone and plant color but giving a recessive brown pericarp color instead of the dominant brown produced by ap. This is also a new allele.
The data on hand indicate that mutations of a to different alleles do not occur with equal frequencies. Although four new alleles have already been found it may be expected that additional new ones will appear as these experiments are continued.
No effect of Dt on any locus other than a has been found. This is true for the unstable pericarp allele (Pvv) as reported before and also for the unstable waxy allele.