CpG Islands (CGIs) are compositionally defined short genomic stretches, which 
have been studied in the human, mouse, chicken and later in several other 
genomes. Initially, they were assigned the role of transcriptional regulation of 
protein-coding genes, especially the house-keeping ones, while more recently 
there is found evidence that they are involved in several other functions as 
well, which might include regulation of the expression of RNA genes, DNA 
replication etc. Here, an investigation of their distributional characteristics 
in a variety of genomes is undertaken for both whole CGI populations as well as 
for CGI subsets that lie away from known genes (gene-unrelated or "orphan" 
CGIs). In both cases power-law-like linearity in double logarithmic scale is 
found. An evolutionary model, initially put forward for the explanation of a 
similar pattern found in gene populations is implemented. It includes segmental 
duplication events and eliminations of most of the duplicated CGIs, while a 
moderate rate of non-duplicated CGI eliminations is also applied in some cases. 
Simulations reproduce all the main features of the observed inter-CGI 
chromosomal size distributions. Our results on power-law-like linearity found in 
orphan CGI populations suggest that the observed distributional pattern is 
independent of the analogous pattern that protein coding segments were reported 
to follow. The power-law-like patterns in the genomic distributions of CGIs 
described herein are found to be compatible with several other features of the 
composition, abundance or functional role of CGIs reported in the current 
literature across several genomes, on the basis of the proposed evolutionary 
model.