During mammalian embryonic development, DNA methylation is an essential process in the regulation of transcription.There are many aberrant methylation in various genomic regions of cloned embryos.

• 哺乳动物种系中，DNA甲基化是胚胎发育期转录调节的必需步骤，除了单拷贝基因序列外，在基因组很多的区域都可以观测到克隆胚胎的异常甲基化。