Studies on the genetically inert region of theX-chromosome ofDrosophila

1. As a result of crossing-over between two differently invertedX-chromosomes anX-chromosome was obtained with a deficiency for a part of its genetically inert region. 2. In theXY males carrying this chromosome, theX andY-chromosomes synapse only in 61·4 per cent. of cases. Each of the unsynapsed chromosomes is lost during disjunction approximately in one-fourth of the cases, not reaching either of the daughter nuclei. 3.XYY males carrying this chromosome produce gametes almost exclusively of theXY andY types. 4. The case studied appears to confirm the views of Muller and Painter concerning the homology of the inert part of theX-chromosome with theY-chromosome, and supports the opinion that few or no gene mutations can at present arise in theY-chromosome (except those of the genebb).