Fusion proteins often referred to as “rosetta stone” occur through an important evolutionary phenomenon called gene fusion. This results in chimeric sequences in one species compared to its unfused individual component sequences in yet another species. Thus, a functional “subunit-subunit” interface in one species has evolved to form a functional “domain-domain” interface in yet another species. Therefore, it is important to describe such events and its possible mechanism with appropriate hypothesis using available structural complexes of some known examples. We describe this phenomenon using illustrations of chimeric protein sequences in comparison with known structures for both fused and unfused forms.