Fig. 4

Nucleotide substitution has higher rate close to indels. a-c: SNP frequencies of indel-flanking sequences. d-f: SNP frequencies of flanking sequences with different distance from indels. 10, 20, 30, 40: 1–10, 11–20, 21–30, 31–40 nt 3′-flanking sequences of indels; − 10, − 20, − 30, − 40: 1–10, 11–20, 21–30, 31–40 nt 5′-flanking sequences of indels. g-i: SNP frequencies of non-flanking sequences of indels. In (a)-(c) and (g)-(i), the difference significance was analyzed by the χ² test. In (d)-(f), the difference in change of SNP frequencies among intervals of flanking sequences was compared with the paired t-test. a, d and g: unigenes mapped to all chromosomal arms; b, e and h: unigenes mapped to chromosomal arms without exogenous fragments; c, f and i: unigenes mapped to chromosomal arms introgressed with exogenous fragments. In e-f: The curve was charted based on the quadratic regression equation through the regression analysis