Fig. 4.
Model of the evolution of an L1 insertion in a population. Data presented here and evidence that hot L1s account for most new insertions (34) suggest that new insertions are derived from hot L1s. Data on alleles of L1A, L1B, L1C, and LRE1 (36, 37) indicate that, after a hot L1 reaches an intermediate gene frequency in the population, it has a significant proportion of cool alleles. As an L1 approaches fixation, mutations produce cool alleles and dead alleles. Shaded box, L1 insertion in chromosomes (lines); black dots, mutations.