CYTOGENETICS OF A MOTH SPECIES WITH A LOW CHROMOSOME-NUMBER, ORGYIA-THYELLINA

While most Lepidoptera have numerous small chromosomes, Orgyia thyelli na has few (n = 11) and relatively big chromosomes. We exploited this situation in a light microscopic study of chromosome morphology in mit osis and in various stages of male and female meiosis.-There is no ind ication of a primary constriction in mitotic chromosomes. Meiosis is c hiasmatic in males and achiasmatic in females. Bivalents in the late f emale pachytene stage have a chromomere pattern of an unusually high d egree of resolution. It is especially suited to test structural homolo gy of synapsed chromosomes in bivalents. The chromomere pattern is hom ologous in the synapsed autosomes but partly differential in the equal ly synapsed sex chromosomes. The female pachytene affords a good basis for cytogenetic investigations in Lepidoptera.