Chicken macrochromosomes contain an endogenous provirus and microchromosomes contain sequences related to the transforming gene of ASV.

Chicken chromosomes from a euploid Marek's lymphoma cell line have been partially fractionated according to size by rate zonal centrifugation in a zonal rotor. DNA-DNA hybridization tests, using unlabeled DNA extracted from gradient fractions and labeled single-stranded, virus-specific DNAs prepared in vitro, indicate that large macrochromosomes harbor the provirus for the endogenous RNA tumor virus of chickens (RAVO), whereas a cellular sequence related to the transforming gene of avian sarcoma virus (ASV) is located in microchromosomes. In support of the method, we have also shown that the single gene for ovalbumin can be assigned to macrochromosomes.