Final answer:
An evolutionarily successful mobile genetic element would integrate into areas of the genome that minimize negative impacts on the host, such as non-coding regions or those with fewer essential genes, and their wide distribution across species implies a role for horizontal gene transfer.
Step-by-step explanation:
An evolutionarily successful mobile genetic element would preferentially integrate into regions of the genome that minimize detrimental effects on host fitness. This often means regions with fewer essential genes or areas with non-coding DNA. For a bacterial IS element, integration is typically within the compact genome where there isn't much 'extra' DNA; thus, most are silent to prevent harmful mutations. In eukaryotes with larger genomes, mobile elements could potentially integrate into a variety of genomic regions due to the presence of more non-coding DNA, which acts as a buffer against possible negative effects. Integration choices may contribute to the high transposon load observed in many eukaryotic genomes. Furthermore, the presence of similar transposons in diverse species suggests that horizontal gene transfer has played a significant role in the distribution of mobile elements.