Why do we study chromosomes? We study chromosomes because their behavior at fertilization and cell division determines the nature of inheritance, and their organization controls the activity of genes [1]. Microscopic observation of chromosomes is important for the study of chromosomes. There are various types of microscopes

and a wide range of techniques for observing chromosomes by microscopy. Recent advances in microscopic technology such as scanning near-field optical microscopy (SNOM) and atomic force microscopy (AFM) have enabled researchers to observe chromosomes on the nanometer scale (see also Chapters 9 to 11) [2-6]. The use of fluorescence-labeled DNA probes in comparative genomic hybridization and fluorescence in situ hybridization (FISH) has made it possible to observe the localization of specific DNA on chromosomes (see also Chapter 6) [7-11]. The diverse range of techniques has provided us with large numbers of chromosome images, processed by various methods at various magnifications. Systematic accumulation of these chromosome images and access to the images using an easy search tool would be beneficial for researchers. There are some text-based databases of chromosomal information [12,13] but no databases of animal chromosome images. We have therefore constructed a database of images of animal chromosomes and bibliographic information on chromosomes and nanotechnologies related to handling, analyzing and sorting of chromosomes. The constructed database, named CHRONIS (CHROmosome and Nano-Information System), is now open to the public on the Web. The database contains a large number of images of animal chromosomes as well as bibliographic information on chromosomes.