Autoradiographic study of transcription and dosage compensation in the sexand neo-sex chromosome of Drosophila nasuta nasuta and Drosophila nasuta albomicans

Cellular autoradiography is used to study the transcription patterns of the polytene X chromosomes in Drosophila nasuta nasuta and D. n. albomicans. D . n. nasuta, with 2n = 8, includes a pair of complete heteromorphic sex chr omosomes, whereas D. n. albomicans, with 2n = 6, has a pair of metacentric neo-sex chromosomes representing incomplete heteromorphic sex chromosomes. The neo-X chromosome has two euchromatic arms, one representing the ancestr al X while the other represents the ancestral autosome 3 chromosomes. The m etacentric neo-Y chromosome has one arm with a complete heterochromatic anc estral Y and the other arm with a euchromatic ancestral autosome 3. The tra nscription study has revealed that the X chromosome in D. n. nasuta is hype ractive, suggesting complete dosage compensation, while in the neo-X chromo some of D. n. albomicans the ancestral X chromosome is hyperactive and the ancestral autosome 3, which is part of the neo-sex chromosome, is similar t o any other autosomes. This finding shows dosage compensation on one arm (X Lx/-) of the neo-X chromosome, while the other arm (XR3/YR3) is not dosage compensated and has yet to acquire the dosage compensatory mechanism.