Genetic regulation of the replication pattern of polytene chromosomes in interspecific hybrids of Drosophila

The sixth chromosome (microchromosome) of D. littoralis changed its replication pattern in nuclei of the salivary gland cells in reciprocal F₁ hybrids between D. virilis and D. littoralis. - To locate the factor (or factors) in the D. virilis chromosomes, which may influence the replication pattern of the sixth chromsome of D. littoralis, we produced hybrid stocks with "synthetic" karyotypes characterized by different combinations of D. littoralis homologous chromosomes and "hybrid" chromosomes. Based on autoradiographical studies of DNA synthesis in "synthetic" karyotypes, it may be concluded that the dominant factor (or factors), which influences the replication of the sixth chromosome of D. littoralis, is located on the homeologous microchromosomes of D. virilis. The possible interrelation between the changed replication pattern of D. littoralis sixth chromosome and its atypical behaviour at early embryogenesis in (D. virilis x D. littoralis) F₁ hybrids is discussed.