Fusion of hypoxanthine phosphoribosyltransferase (HPRT)(-) rat hepatoma cells with HPRT(+) human fibroblasts yielded hybrid clones that grew in HAT selective medium and contained all the rat chromosomes and one to nine human chromosomes. Among the retained chromosomes was the human X chromosome. In all clones backselected in medium containing 8-azaguanine, human X chromosome was absent. Electro...

T HE PROFOUND alteration in human erythrobbasts in folic acid or vitamm B12 deficiency is manifest to an important degree by the appearance of the interphase nuclear chromatin in the megaloblastic cells. This is reflected in the appearance of the individual chromosomes, and it is generally agreed that the chromosomes of megaloblasts differ in morphologic details from those of normoblasts. Rohrt...

From observations on the partial disintegration of isolated human metaphase chromosomes we propose that human metaphase chromatids have a rather simple organization based on the folding and coiling of a long, regular, hollow cylindrical structure with a diameter of about 4000 A. This cylindrical structure, the unit fiber, is postulated to be a super-solenoid formed by the coiling of a 300 A sol...