Genomic imprinting is an epigenetic mechanism that results in monoallelic 
expression of genes depending on parent-of-origin of the allele. Although the 
conservation of genomic imprinting among mammalian species has been widely 
reported for many genes, there is accumulating evidence that some genes escape 
this conservation. Most known imprinted genes have been identified in the mouse 
and human, with few imprinted genes reported in cattle. Comparative analysis of 
genomic imprinting across mammalian species would provide a powerful tool for 
elucidating the mechanisms regulating the unique expression of imprinted genes. 
In this study we analyzed the imprinting of 22 genes in human, mouse, and cattle 
and found that in only 11 was imprinting conserved across the three species. In 
addition, we analyzed the occurrence of the sequence elements CpG islands, C + G 
content, tandem repeats, and retrotransposable elements in imprinted and in 
nonimprinted (control) cattle genes. We found that imprinted genes have a higher 
G + C content and more CpG islands and tandem repeats. Short interspersed 
nuclear elements (SINEs) were notably fewer in number in imprinted cattle genes 
compared to control genes, which is in agreement with previous reports for human 
and mouse imprinted regions. Long interspersed nuclear elements (LINEs) and long 
terminal repeats (LTRs) were found to be significantly underrepresented in 
imprinted genes compared to control genes, contrary to reports on human and 
mouse. Of considerable significance was the finding of highly conserved tandem 
repeats in nine of the genes imprinted in all three species.