A survey of seedling mutants isolated from the mutator line (Mu) indicates that 15% are mutable. Because mutability is a characteristic of mutants influenced by controlling elements, the relationship between Mu and other mutable systems such as Dt, En and Mp is of interest. This relationship can be tested in two ways: 1) by determining if controlled alleles of the above systems respond to Mu and 2) by using mutable controlling element stocks in a manner analogous to the Mu line to test for an increase in the mutation rate. Preliminary results of the latter test are presented here.

Plants were self-pollinated and crossed to a standard line, and a sample of the outcrossed seeds were self-pollinated. The following results were obtained:
 

Stock	Number of outcrosses tested	Total number of plants	Number of mutants	% mutations
Dt	8	342	0	0
En	8	343	0	0
MP	8	318	0	0
Total	24	1003	0	0

It is clear that there is no dramatic increase in mutation rate in these stocks.

Peter Mascia and D. S. Robertson

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