Tests for Recombination amongst Three Lethal Mutations

N T H E mouse a peculiar relation exists amongst three lethal mutations I which produce similar effects on development. Animals which inherit two doses of the same lethal die as early embryos, while those which inherit one dose each of two different lethals of this group may be viable. This is the result to be expected when the lethals involved occupy different loci, but in the present case the different lethals have shown no recombination with each other and may therefore be considered either as unilocal or as occupying different loci amongst which crossing over is prevented. If the first alternative were proved to be correct, there would be revealed a type of complementary interaction amongst alleles which could not be reconciled readily with theories which regard changes a t the same locus as purely quantitative in character. It is a fact, however, that the mutations in question have certain other effects in common and thus resemble other series of multiple alleles, the members of which appear to differ in quantity of effect. The first step in resolving this contradictory situation is to determine whether or not the mutations involved are unilocal. In the present paper the question will be examined as to whether or not any recombination occurs in animals heterozygous for different members of this group of lethals.