CHEMICAL ALTERATION OF CROSSING-OVER FREQUENCY IN CHLAMYDOMONAS

Abstract
Variations in crossing-over frequency have been shown to follow treatment of cells of biochemical mutant strains of C. reinhardi with a chelating agent or with MnCl2. The frequency of crossing over was increased by these treatments in two of three chromosome intervals tested. The effects of both agents were reversed by subsequent incubation of treated cells in high concentrations of calcium and magnesium ions. It is suggested that the action of MnCl2 may involve the replacement of Mg by Mn. The sensitivity of crossing over in C. reinhardi to ionic environment is consistent with the theory that chromosomes are composed of macromolecular unit particles linked together by divalent ions.

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