Spermatogonial exchange involving the X but not the y chromosome inDrosophila Melanogaster

Summary The distal uninverted portion of In(1)sc⁸, which carriesy ⁺ andac ⁺, is occasionally lost during spermatogonial divisions. This is accomplished by exchange between the protion of the proximal heterochromatin that has been removed distally by the inversion and some other heterochromatin in the complement (see alsoLindsley 1955b).. The majority of the recombiants recovered from males carrying In(1)sc⁸ arise through exchange with the Y chromosome (12/15). The majority of the recombinants recovered from males carring In(1)sc^8L, EN^R, which is characterized by a heterochromatic second arm, do not arise through exchange with the Y chromosome (18/22). The absolute frequencies of Y involvement with In(1)sc⁸ (7/105067) and In(1)sc^8L, EN^R,(2/38588), however, are comparable. The heterochromatic constitution of the recombinants examined is consistent with the hypothesis that an observed excess of recombinants recoverred from In(1)sc^8L, EN^R as compared with In(1)sc⁸ is accounted for by Y independent recombinants and is the consequence of exchange between the second heterochromatin arm of In(1)EN^R and the distal heterochromatin of In(1)sc^8L. A maximum of six different regions of exchange between these two regions may be inferred from the constitution of the recombinants. This inference is considered to support the hypothesis that pairing and exchange between heterochromatic regions are not strictly homologous.With 6 Figures in the TextOperated by Union Carbide Nuclear Company for the U.S. Atomic Energy Commission.Part of the material was presented to the Graduate School of the California Institute of Technology in partial fulfillment of requirements for the degree of Doctor of Philosophy supported by an Atomic Energy Commission predoctoral fellowship. Further experimentation has been pursued under a National Research Council postdoctoral fellowship at the University and under a National Science Foundation postdoctoral fellowship at the University of Missouri. Experimentation was completed at Oak Ridge.