Figure 3.
Phylogenetic tree of Alu subfamilies. Human Alu elements having intact head and tail were randomly selected from both the GenBank database and the on-line database of Alu pairs (http://dir.niehs.nih.gov./ALU/). The tree was made by the neighbor-joining method (20). Distances were calculated with Kimura's two-parameter method (21). The poly(A) tails of sequences were not used in tree-making. The sequence of an AluJb element, which belongs to the old AluJb subfamily, was used as an outgroup. The average age of AluJb, AluSq, AluY, and AluYb8 subfamilies has been estimated at 81, 44, 19, and 3 million years, respectively (ref. 22). The Alu elements shown in Fig. 1 are represented by Hs sahAluY, Pt sahAluSq, Gg sahAluSq, and Mm sahAluSq. msAluY indicates the sequence most similar to the one of sahAluY. Hs, Homo sapiens; Pt, Pan troglodytes; Gg, Gorilla gorilla; Mm, Macaca mulatta.