NON-MENDELIAN FEMALE STERILITY IN DROSOPHILA MELANOGASTER: HEREDITARY TRANSMISSION OF I FACTOR

Abstract

Systematic crosses between various strains of Drosophila melanogaster lead in some cases to partly sterile F₁ females. Two main classes of strains, inducer and reactive, may be recognized on the basis of the fertility of F₁ female progeny. Females which may show incomplete sterility (SF ♀) arise only when reactive females are crossed with inducer males, other crosses, including the reciprocal, producing only fertile F₁ females. SF sterility appears as the result of an interaction between two factors, R brought into the initial cross by the reactive mother and maternally inherited, and I brought by the inducer father. The present paper reports on the hereditary transmission of I factor. It is shown that when transmitted through heterozygous males, bearing chromosomes of both inducer and reactive origin, I factor may be strictly linked to any one of the three major chromosomes of inducer strains. Such chromosomes carrying I factor were called inducer chromosomes. When transmitted through heterozygous females, this Mendelian behavior fails to hold, and non-inducer chromosomes coming from reactive strains may become inducer independently of the production of recombined gametes. This phenomenon was called chromosomal contamination. This contamination occurs even between nonhomologous chromosomes.