Stability of X chromosomal inactivation in human somatic cells transformed by SV-40

Clones of fibroblasts from a G6PD A heterozygote transformed with SV-40 did not express the G6PD silent allele in the transformed heteroploid cultures. In addition, transformed fibroblasts from a woman heterozygous for both G6PD A and HGPRT deficiency, subjected to selective pressure, did not reveal a single cell expressing either silent allele. Since the incidence of sex chromatin was significantly lower in these cells after transformation, it is likely that the loss of sex chromatin reflects the loss of the inactive X-chromosome at an early stage following transformation.