Structural mutants of the W chromosome in Ephestia (Insecta, Lepidoptera)

Structural mutants of the W chromosome that are kept in laboratory strains are described using light and electron microscopic techniques. The series comprises a translocation, a deficiency, fusions, and W fragments. - Conclusions drawn from the mutants are the following: At least one half of the W serves no vital function and is dispensable. Female sex determination, if the W is involved at all, rests on the other half. The amount and form of heterochromatin in somatic interphase nuclei depends on the amount and location of the W chromosome material. The W inactivation in somatic cells does not spread to attached autosomal segments.