TETRAPLOID FEMALES IN MORMONIELLA

Abstract

IN the wild-type hymenopteron, Mormoniella, it has been shown that five atelomitic chromosomes are characteristic of the male and that unlaid eggs have five bivalents, indicating that normal diploid females have ten chromosomes (WHITING 1968). In the polyploid stocks, the diploid males, identified by complementary allelism, have ten chromosomes ( PENNYPACKER 1958). Investigations on polyploidy by use of R-locus markers have hitherto been strictly genetical. A very few tetraploid females which produced no progeny were found before 1960, after which time study of tetraploidy was deferred until the present project was undertaken. The purpose of this project was (1 ) to obtain tetraploid females, (2) to determine whether they were fertile, (3) to see if they showed any obvious structural differences from diploid or triploid females, and (4) to study some aspects of meiotic behavior. Recombination between the two mutant factors designated 0 and S does not occur at the complex locus R. Thus oyster eye color is oy-l-, scarlet is +.st, this system being devised from the facts that oyster by scarlet produces wild-type females, oy.+/+.st, and that the male progeny of these females are oyster and scarlet. Wild type, +.+, and oyster scarlet, oy.st, are not produced. Polyploidy has been recorded as occurring by mutation three times (WHITING 1960). In each case the mutant was distinguished from its siblings by its wild-type eye color, and wild-type descendent females were of very low fecundity although laying many eggs. These females were triploid, their eggs, for the most part, aneuploid and inviable. The few euploid eggs of triploid females, if unfertilized, produce haploid and diploid males.