Inhibition of Polytene Chromosome Formation in Phaseolus by Polyploid Mitoses

Abstract

The course of the cell cycles during the early development of the suspensor in Phaseolus coccineus and Ph. vulgaris is a factor influencing the occurrence of polytene chromosomes within the mature, highly endopolyploid nuclei. If there is a continuous sequence of endomitotic cycles, giant chromosomes arise. If the early endopolyploidization is interrupted by a polyploid (4x, 8x, or 16x) mitosis, the nuclear structure remains diffuse, also during the subsequent endomitotic growth of the nuclei.
A scheme is given to demonstrate that a specific short-cut of the cell cycle is necessary for the origin of polytene chromosomes in general.