Distribution of vsp genes along chromosome 4. The contigs were initially assigned to individual chromosomes by mapping end-sequenced BACs to PFG separations of chromosomes and subsequently refined by optical mapping. Chromosome 4 is the most densely populated with vsp genes (29/Mb). Each vsp gene is noted by a vertical line, which is above the horizontal chromosome line for those with a forward orientation in relationship to the chromosome direction and below for those oriented in a reverse direction. The contigs from Assembly 14  are shown below with arrows indicating the orientation of the contig. Vsp s with tandem repeats are noted with "TR" and those present in linear arrays are shown as filled in boxes with each section representing one vsp gene. TT indicates tail to tail arrangement.