This article focuses on a study related to rapid and efficient detection of transgene homozygosity by FISH of mouse fibroblasts. The generation of homozygous transgenic mice has a number of extremely useful applications in modern biological research. First, a homozygous transgene is generally expressed at a higher level when compared with the corresponding hemizygous state and often leads to altered phenotypes. Several methods have been developed for the identification of homozygous transgenic mice among the offspring from crosses between hemizygous animals.