What factors affect the gain or loss of introns?

The variations in the frequency of gaining or losing introns among different eukaryotes occur due to differences in the rates of random mutations leading to these events and the likelihood of these mutations becoming permanently incorporated into the genome. These mutations may interfere with established splice sites or regulatory sequences involved in splicing, such as intronic and exonic splicing enhancers and silencers. They can either disrupt existing regulatory elements, or activate previously dormant ones or create new ones. Additionally, introns can be acquired or lost over the course of evolution. Studies have revealed thousands of cases where new introns have appeared or existing ones have disappeared. Natural selection can act on introns. Introns that play crucial roles in gene regulation or splicing efficiency may be more likely to be retained. The loss of introns may happen when positive selection is not occurring. Researchers have identified two main mechanisms responsible for the loss of introns, which include Reverse Transcriptase-Mediated Intron Loss (RTMIL) and genomic deletions.