This book is focusing on dynamics of de-novo methylation in embryonic genes during development and tissue differentiation and its correlation with the expression of genes in laboratory mouse.DNA methylation is an epigenetic mark present on genomic DNA. Its key role lies in regulation of gene expression. During embryonic development, the gametic methylation is removed within the first few cleavage divisions, and for most genes a fresh wave of methylation occurs during post- implantation development, making DNA methylation an integral part of cellular differentiation and differential gene function. How does the fresh wave of methylation set in the genome is not well understood. Patterns of methylation of the genes studied are distinct from those DNA sequences which methylate pre- and post-implantation, both in terms of the timing and spreading.