A special type of multigene family is implicated in the movement of gene families and gene family members. LINE (Long INterspersed Elements) and SINE (Short INterspersed Elements) families are highly repetitive DNA sequences spread all throughout the genome. The LINEs contain a sequence that encodes a reverse transcriptase protein. This protein aids in copying the RNA transcripts of LINEs and SINEs back into DNA, and integrates them into different areas of the genome. This self-perpetuates the growth of LINE and SINE families. Due to the highly repetitive nature of these elements, LINEs and SINEs when close together also trigger unequal crossing over events which result in single-gene duplications and the formation of gene families.
