Résumé
To examine the evolutionary influence of gene conversion on DNA base composition, I analysed an exhaustive dataset of histone paralogous genes from human and mouse. I show that those gene copies that belong to subfamilies of very similar sequences (presumably undergoing gene conversion) have a higher GC content than unique gene copies (presumably not undergoing gene conversion). Thus, it seems that gene conversion is a biased process that tends to increase the DNA GC content, a conclusion that has implications for the evolution of isochores in vertebrates.