Isolation and characterization of sex chromosome rearrangements generating male muscle dystrophy and female abnormal oogenesis in the silkworm, Bombyx mori.

Abstract  In deletion-mapping of W-specific RAPD (W-RAPD) markers and putative female determinant gene (Fem), we used X-ray irradiation to break the translocation-carrying W chromosome (W Ze ). We succeeded in obtaining a fragment of the W Ze chromosome designated as Ze W, having 3 of 12 W-RAPD markers (W-Bonsai, W-Yukemuri-S, W-Yukemuri-L). Inheritance of the Ze W fragment by males indicates that it does not include the Fem gene. On the basis of these results, we determined the relative positions of W-Yukemuri-S and W-Yukemuri-L, and we narrowed down the region where Fem gene is located. In addition to the Ze W fragment, the Z chromosome was also broken into a large fragment (Z1) having the + sch (1-21.5) and a small fragment (Z2) having the + od (1-49.6). Moreover, a new chromosomal fragment (Ze WZ2) was generated by a fusion event between the Ze W and the Z2 fragments. We analyzed the genetic behavior of the Z1 fragment and the Ze WZ2 fragment during male (Z/Z1 Ze WZ2) and female (Z1 Ze WZ2/W) meiosis using phenotypic markers. It was observed that the Z1 fragment and the Z or the W chromosomes separate without fail. On the other hand, non-disjunction between the Ze WZ2 fragment and the Z chromosome and also between the Ze WZ2 fragment and the W chromosome occurred. Furthermore, the females (2A: Z/Ze WZ2/W) and males (2A: Z/Z1) resulting from non-disjunction between the Ze WZ2 fragment and the W chromosome had phenotypic defects: namely, females exhibited abnormal oogenesis and males were flapless due to abnormal indirect flight muscle structure. These results suggest that Z2 region of the Z chromosome contains dose-sensitive gene(s), which are involved in oogenesis and indirect flight muscle development. [ABSTRACT FROM AUTHOR]