Abstract: To achieve re-totipotency in the process of animal somatic cell cloning, donor cells which were in high degree of methylation status needed to change for the non-methylation status of embryonic cells. DNA Methyl-transferase inhibitor（5-aza-dc）was used to treat donor cells to seeking for the best concentration of 5-aza-dc in this experiment. With this concentration，we could not only reduce the somatic cell nucleus for the methylation status but also have no effect on the number and structure of chromosomes, thereby providing a improved methods for somatic cell cloning efficiency. In the experiment, cow fibroblasts were treated with different concentration 5-aza-dc for 72 h and then used conventional method of chromosome karyotype analysis to prepare fission phase of chromosome and detect the number and structure of chromosome. The results as follows：There were not significant aberration of chromosome with lower concentration (0.005 μmol/L and 0.01 μmol/L) 5-aza-dc (P＞0.05). The chromosome can maintain normal shape. The experimental group(0.03 μmol/L and 0.05μmol/L)could significant induce the aberration of chromosome(P＜0.05). The aberration rate of chromosome was the highest in group treated with 0.1 μmol/L 5-aza-dc and was much more significant than the control group（P＜0.01）. In a word, these results indicated that there was no effect of chromosome structure and its number when the donor cells were treated with 0.005 μmol/L and 0.01 μmol/L 5-aza-dc for reducing the DNA methylation level .While in a high concentration, the 5-aza-dc could induce higher aberration of chromosome and could not used in animal somatic cell cloning production.

Key words: DNA Methyl-transferase inhibitor; cow fibroblasts; chromosome