The existence of whole genome sequences makes it possible to search for global 
structure in the genome. We consider modeling the occurrence frequencies of 
discrete patterns (such as starting points of ORFs or other interesting 
phenomena) along the genome. We use piecewise constant intensity models with 
varying number of pieces, and show how a reversible jump Markov Chain Monte 
Carlo (RJMCMC) method can be used to obtain a posteriori distribution on the 
intensity of the patterns along the genome. We apply the method to modeling the 
occurrence of ORFs in the human genome. The results show that the chromosomes 
consist of 5-35 clearly distinct segments, and that the posteriori number and 
length of the segments shows significant variation. On the other hand, for the 
yeast genome the intensity of ORFs is nearly constant.