Chromosomal distribution and segmental duplication events for Arabidopsis IQD genes. The five chromosomes are indicated by Roman numerals and the centromeric regions by ellipses. Deduced chromosomal positions of the IQD genes are marked by horizontal bars and gene identification numbers (last five digits only). The scale is in megabases (Mb) and is adapted from the scale available on the TIGR database (see Materials and methods). Non-hidden duplicated chromosomal segments  that contain at least one retained IQD gene pair are color-coded. In three such segments (blue, brown, light blue), one sister IQD gene has been lost. Additional non-hidden duplicated segments that have lost sister IQD genes are shown in white and both segments are labeled with the same Arabic numeral. The duplicated segments of one such event (number 3) have likely experienced reciprocal IQD gene losses as the remaining genes, At3g22190 and At4g14750, are only distantly related (see Figure 1a). Numbers in italics at left indicate the estimated age (Myr) of the duplication event according to Simillion at al. ; the age estimates are given only once in the order of IQD gene location beginning with chromosome I.