Proof That Bar Changes to Not-Bar by Unequal Crossing-Over

Abstract

For a final proof of Sturtevant''s theory of unequal crossing-over at the bar locus a demonstration of both resulting chromosomes, double bar and +, is desirable. This was accomplished. In a mating of attached-X [female][female] homozygous for bar with yellow [male][male], a [female] occurred showing the narrow eyes characteristic of flies having BB/ +. It was proved that this was her actual composition by mating to yellow [male][male]- If she had been either BB/B (only one chromosome a crossover) or B/B accentuated by modifiers, no round eyed progeny would result. About 5% round would be expected if she were BB/ +. An F1 and an F2 giving approximately this proportion proved that BB/+ was the correct interpretation.