Figure 3

Age distribution of C2H2 ZFs in chromosome 19 (blue curve) and in the remainder of the autosomes (red curve). The area below each curve describes the total number of zinc-fingers in the corresponding time interval. The total number of C2H2 domains in chromosome 19 is 3513, whereas the remainder of the autosomes contain 4567 zinc-finger domains. The age of a particular C2H2 sequence is defined as the time of the most recent duplication event associated with such C2H2 domain. The duplication times are computed as the branch lengths of a phylogenetic tree and the units of time consist of the fraction of nucleotide substitutions (f.n.s.) (see ‘Analysis of C2H2 motifs in Materials and Methods’). The high density of zinc-fingers for times smaller than 0.2 f.n.s. in chromosome 19 denotes a recent burst of duplications of zinc-fingers on this chromosome. This contrasts with the expansion of C2H2 domains on the remainder of the autosomes which, although they span 98% of all autosomal DNA, they only contribute a third of all recent duplications of zinc-fingers. This huge expansion of C2H2 zinc-fingers in the human lineage is specific to chromosome 19 and probably occurred during mammalian evolution