GENETIC RECOMBINATION INCOPRINUS. I. ITS PRECISE TIMING AS REVEALED BY TEMPERATURE TREATMENT EXPERIMENTS

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Abstract
A meiotic system that facilitates comparative genetic analysis of recombination and cytological observations of meiosis and chromosome structure by light and electron microscopy is described. Both high (35°C) and low (5°C) temperature treatments can increase genetic recombination in Coprinus lagopus. Cold treatment appears to be more effective than heat treatment. The maximum recombination increase is 220% by cold, and 95% by heat treatment. As revealed by the temperature-treatment experiments, the time that recombination can be modified is determined precisely at a stage defined by light microscopy as pachytene, this period being estimated to be about 4 hr. Temperature treatments do not cause asynapsis or desynapsis. In fact, the chromosomes are very well paired after treatments, and pairing appears to be closer than, that of the controls. It is suggested that temperature treatments induce 'exchange pairing' which is defined as a molecular event leading to the formation of the hybrid DNA.