PCR analysis testing for the presence of an LTR retroelement feature in two genes, Cht3 and cathD , across three representative Drosophila strains. A negative image is presented for visual clarity. Three PCR reactions were performed per strain, per gene. M = 1 kb ladder, M2 = 0.1 kb ladder. (A) An Antonia LTR fragment is fixed in the intron of the heterochromatic Cht3 gene in all 12 tested strains (only three shown). Cht3-G = cht3 primers (f+r), expected product= 488 bp. L = Antonia LTR primers (f+r), expected product= 272 bp. G2/L = cht3(f2) + Antonia LTR (r) primers, expected product= 3022 bp. (B) A full-length Burdock LTR retrotransposon is found to be associated with cathD only in the sequenced y; cn bw sp strain. cathD – G = cathD primers (f+r), expected product = 461 bp. L = Burdock primers (f+r), expected product = 280 bp. G/L = cathD(f) and Burdock element (r), expected product= 1139 bp.