Gene retroposition is known to contribute to patterns of new gene evolution and evolution of novel traits. However, most of the previous studies were conducted in comparisons between species, and less attentiaon has been paid to the evolutionary dynamics and patterns of very recently derived retrocopies that are still polymorphic within natural populations. Herein, we used house mouse as the study system to trace the origin of evolutionary fate of newly arrived retrocopies. We found the primary rate of retroposition is orders of magnitude higher than the long-term rate. Comparisons with single-nucleotide polymorphism distribution patterns in the same populations show that most retroposition events are deleterious. Transcriptomic profiling analysis shows that new retroposed copies become easily subject to transcription and have an influence on the expression levels of their parental genes, especially when transcribed in the antisense direction. These results imply that the impact of retroposition on the mutational load has been highly underestimated in natural populations. Despite of their largely deleterious effects, we also found a small subset of new retrocopies with rapid increasing frequency in populaions. They were likely involved in a recent adaptation process, evidenced by the strong signature of posive selection. Overall, our study shows the dual roles of gene retrocpies at population scale.
Tracing the origin and evolutionary fate of recent gene retrocopies in natural populations of the house mouse