Endoreduplication induced by Colcemid in human lymphocytes. Autoradiographic study of DNA synthesis in diplochromosomes

Abstract

A study has been made of some characteristics of cells with endoreduplica­tion induced by Colcemid in cultures of human lymphocytes, thc possible mechanisms of this induction being discussed. The said cells are morphologically similar to those which appear spontaneously, but with a greater incidence of breaks in chromatides and translocations. The secondary constrictions and the difference in size between homolo­gues are morphological characters which are transmitted in the reduplication of the chromosomes, as is deduced from the study of these characters in the diplo- and quadruplochromosomes.

When the endorcduplications are marked with Timidine-H3 during their first period of DNA synthesis, the diplochromosomes are more apt to have the two external chromatides marked, and the quadruplochromosomes the infernal, of the two brother chromosomes placed peripherally. These data seem to point to the existence of a special disposition, ordered and not haphazard, of the synthetized DNA subunities in successive reduplications. Curiously, such a dispo­sition does not coincide with that which is habitually employed in the redupli­cation schemes of DNA at the molecular level.