COMPARABLE MUTANT EYE COLORS IN MORMONIELLA AND PACHYCREPOIDEUS (HYMENOPTERA: PTEROMALIDAE)

In such forms as Drosophila and Habrobracon visible mutations from the wild type are, for the most part, recessive and each change is usually thought to be of a simple nature involving modification of a single trait. Further study, however, reveals that minor modifications often accompany the major difference, that less obvious changes are associated with the trait for which the mutation is named. In some cases the gene is obviously pleiotropic, very different structures being affected such as bristles and wings or legs and antennae (Caspari, 1952). When different mutations occur at a .single locus forming a multiple allelic series, the genes may usually be arranged in order of dominance of the traits or, if blending occurs in the compounds, in order of increasing effects. This suggests a single type of material differing quantitatively in the different alleles. Many genes, however, are not single physiological units or types of substance but appear to consist of different elements governing different traits. In such cases the gene or locus is said to be complex. The unity of complex genes consists merely in the fact that their hypothetical elements segregate in meiosis without recombing. A pair of complex genes may exhibit complete or partial complementarity in their compound if dominance of their elements is in opposite directions. Complementarity is illustrated by the blood groups when alleles determine the presence of different antigens. Antigens are dominant, antibodies recessive. The compound shows both antigens but neither antibody.