R-locus eye color factors in Mormoniella.

I N the chalcidoid wasp Mormoniella vitripennis (Walker) there has been formed by mutation a series of multiple allelic genes, each differing from wild type in one or more factors. The term “factor” is here used in an inclusive sense to denote anything which has an effect on development or which can in any other way be detected. The genes in this “R’ series are pleiotropic, unifactorial, bifactorial, trifactorial, etc., according to the number of their factors in which they differ from wild type. Any one factor may have one or more mutant states which are alternative to each other. The alternative states of the factors form subseries within the series of allelic genes, so that, theoretically at least, the total number of possible alleles would be equal to the product of the various states of each of the factors. Factors 0, S and M: Two of the eye-color factors are characterized by relatively high frequency of mutation, either spontaneous or radiation induced. Factor 0 mutates to colorless, oyster-white, and factor S mutates to scarlet. The compound wild-type females, oy.+/+.st, produce oyster and scarlet sons in equal numbers from their unfertilized eggs. The double recessive gene, oy.st, is formed not by recombination of the factors, but by mutation in stock already recessive for one factor. Mutations comparable to oyster and scarlet have been obtained in a related chalcidoid species, Pachycrepoideus dubius Ashmead, belonging to the same family Reromalidae as Mormoniella (WHITING 1954). Here also the two genes act as complementary alleles and the rate is high, five scarlet, six oyster among 1433 sons of X-rayed (2500r) females. It has been suggested that an R region may be common to the group. The 0 factor produces some enzyme which, acting alone on chromogen, produces red pigment while S determines the presence of a secondary enzyme which may unite with 0. The compound enzyme O-S combines with chromogen to form dark pigment. The proximity of 0 and S in the R region may facilitate production of compound enzyme O S , leading to chromatogenesis. Mutations to oyster and to scarlet are relatively stable. Gene descendants of a certain mutated gene, ti-277 ( t i s t ) (tinged eyes) are characterized by an unstable condition of factor 0 giving a range of “red” eye colors from reddish brown (rdh) near wild type, through mahogany ( m h ) , dahlia (da ) , tomato ( to ) , apricot (up) , orange ( o r ) , peach ( p e ) to tinged ( t i ) near oyster white, None of these relatively frequent spontaneous mutations is accom-