Gene Action in the X-chromosome of the Mouse (Mus musculus L.)

Ohno and Hauschka¹ showed that in female mice one chromosome of mammary carcinoma cells and of normal diploid cells of the ovary, mammary gland and liver was heteropyknotic. They interpreted this chromosome as an X-chromosome and suggested that the so-called sex chromatin was composed of one heteropyknotic X-chromosome. They left open the question whether the heteropyknosis was shown by the paternal X-chromosome only, or the chromosome from either parent indifferently.