Pulsed-field gel electrophoresis and alkaline pulsed-field gel electrophoresis were used to analyze the chromosome DNAs of Ashbya gossypii and two kinds of its mutant strains CMG and JMG,which were obtained by γ-ray and Helium-Neon laser irradiation,respectively.The experiments resulted in the conclusions that AG contains five chromosome DNAs;and that no double-stranded breaks or loss of large DNA fragments but alkaline labile sites existed in both the mutant strains.