In this manuscript the current status of direct visualization of gene locat
ion on chromosomes was reviewed by considering 5 aspects as follows: princi
ple of in situ hybridization (ISH) method, historical perspective of mappin
g genes by in situ hybridization, improvement in the sensitivity of fluores
cence in situ hybridization (FISH), visualization of location of useful gen
es on chromosomes, and prospects for visualization of useful genes.