A genetic linkage study of W-chromosome-autosome fusion, breakage, and kinetic organization of chromosomes in Ephestia (Lepidoptera)

In a search for genetic markers of W-chromosome-autosome fusions in Ephestia, two closely linked autosomal markers, ml and Us, were found to show sex linkage in several families of chromosome mutant strains. In these families, the wild-type allelomorphs, ml⁺ and US⁺, label the autosome that is translocated to the W chromosome. With ml ('musterlos') a sex dimorphic strain could be established in which males (ml/ml) have patternless wings and females (ml⁺/ml) have the normal wing pattern.-Using these genetic markers, stability of the fusion chromosome was studied. Recurrence to autosomal inheritance of the marker occurs at a considerable rate. In two chromosome fusion strains, a cytogenetically detectable breakage of the fusion giving rise to a wild-type-like W chromosome was the predominant cause for the recurrence of the marker to autosomal inheritance. In a third strain a more complicated chromosome rearrangement was the predominant cause: the translocated autosome was replaced by a non-homologous one, presumably after a cytogenetically undetectable breakage event of the original fusion. - The high rate of breakage suggests that the fusion chromosomes are dicentrics, a situation not compatible with a typical holokinetic organization of Lepidoptera chromosomes.