There are different types of processes that may be accountable for intron insertions with/without events responsible for the primordial emergence of spliceosomal introns. Proto-splice site is the hotspot for these intron insertions as other insertions may not be compatible with life in general. The minimal requirement for proper spliceosomal performance is the presence of both authentic cis splice signals and core trans factor, The function of spliceosomes does not depend on how introns have evolved, which could be either by the insertion of intron sequences, probably created by expansion of short simple repeats or more complex repetitive elements , or by intronisation of exonic sequences due to point mutations . Genome compaction in many actinopterygians after the fish-specific whole genome duplication is considered to have promoted intron insertions in these fishes . DNA double-stranded breaks and recombination, which involve repair and recombination processes are essential components of genome compactness. Furthermore, intron insertions are now considered to be resultant of error-based repair of DBSs that is predominantly mediated by non-homologous end joining as recently reviewed . We report that missing repeats in introns from pufferfishes are most likely due to a higher degree of genome compactness in the tetraodontidae lineage when compared to the medaka/stickleback lineage . Gene level novelties are created either by whole genome duplication or by segmental duplications, which may conceivably lead to the gain of novel introns, as an unaffected gene copy remains within the genome. The appearance of novel introns in the MC5R and MC2R cannot be directly coupled to gene or genome duplication, as none of these introns are found in MC receptors from D. rerio, which diverged at a time period closer to the fish-specific genome duplication event than the other rayfinned fishes selected in this study. Whether intron insertions occur preferentially in multi-gene families or take place at random is still controversial . A recent study of multiple intron gains in serine protease inhibitor superfamily in the lineages of selected ray-finned fishes illustrates similar results where the same four fishes have intron gains in selected serpin genes. Vertebrate serpins are classified by the presence of MG132 conserved intron positions, which are well-documented and are used in classification of vertebrate serpins into six groups V1�CV6 . In contrast, the majority of MC receptors are primarily described by intron-less gene structures. However, it is interesting that genes with novel intron from both these superfamilies encode for single domain protein with peptide length of 300�C 400 amino acids with additional N-/C-terminal NVP-BEZ235 extensions. Upon comparisons of novel introns from both these superfamilies, we found that reported novel introns from serpins are considerably smaller than those of MC receptors.