Figure 1

Frequency of closely spaced FAPs. (A) Human adjacent FAP frequency versus the spacer size (bp) separating the two members of the FAP. The number of inverted pairs (blue and green lines) is much lower than the number of direct pairs (red and black lines) when the spacer has a size ≤ 24 bp (I:D = 0.076); (B) Spacer lengths within 24 to 36 bp define the only region within the human genome where head-to-head (inverted) FAPs outnumber either type of direct oriented FAPs. Bp: base pair; FAP: full-length Alu pair.