4. Inversion in long arm of chromosome 3.

The breakage points in paracentric inversion 3a are just to the left of the knob in the long arm and very near the end so that in the inverted chromosome the knob lies close to the distal end of the long arm. The locus of Ragged is to the left of the proximal break while lg₂, A and et all lie within the inverted region and show almost complete linkage with one another and with the inversion. Owing to the greater length of the inversion some two‑strand doubles occur. This inversion promises to be of some value in connection with the study of mutation at the A locus since crossing over is effectively suppressed in regions lying on either side.