Chimpanzee And Human Intron Comparison Reveals Functional Constraints And Complex Evolution

The principle that different DNA sequence conservation reflects variation in functional constraint is one of the most important foundations of comparative genomic approach. According to this principle, orthologous genes were chosen from chimpanzee and human species in order to realize intron evolution and functional constraints since these close relatives diverged. We calculated intron length, GC content, insertion and deletion (indel) events and found that characteristics between introns and exons were totally different, which reflected discrepancy of their function and evolution. In this paper, following results were obtained: (1)longer size and lower GC content in introns than exons were relative to their major functions in human and chimpanzee genomes, (2)strong selection that acted on shorter introns to retain minimal size for proper splicing was detected, (3) short indel fragments correlated positively with their compositions in introns and did not randomly happen, (4) introns worked as an enhancer for recombination to reduce Hill-Robertson effects between weakly selected mutations influenced selection efficiency. Overall, all results above suggest that selective constraint is driving intron evolution at a certain extent to generate genetic features we have observed but functional constraints may compel mutation and selection to achieve dynamic balance.