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. 2004 Apr 1;32(6):1973–1981. doi: 10.1093/nar/gkh509

Figure 1.

Figure 1

Figure 1

Figure 1

Figure 1

IR examples. Open boxes represent the coding region of a gene, and gray boxes represent non-coding regions. Small black boxes represent the IR region of the gene of interest. (a) A directon is a collection of adjacent genes on the same DNA strand with no intervening genes on the complementary strand. A singleton is a directon made up of only one gene. Definition of an IR: (b) at the start of a directon, both genes share the same IR but coded by different strands; (c) when the positive strand codes two consecutive genes; and (d) when two consecutive genes are coded by the negative strand.