Distribution of tetranucleotide repeats in genomic and EST sequences of cucumber and seven other plant species. Frequency values are expressed as number of repeats per million base pairs of sequence. Species are arranged in order to their phylogenetic relationship with cucumber. All species considered, repeats of AAAT (T = 3.46, P = 0.009), AATT (T = 3.90, P = 0.005), AAAC (T = 2.71, P = 0.017), ACAT (T = 3.07, P = 0.008), AACT (T = 4.04, P = 0.001), AATC (T = 3.67, P = 0.003), and AATG (T = 2.25, P = 0.041) were significantly more frequent in genomic- than in EST sequences, whereas the AACC (T = 2.39, P = 0.031) tetranucleotides were more abundant in EST data. Refer to Additional file 1 (supplement Tables S2a and S3a) for details on frequencies of individual tetranucleotide motifs.