Figure 2.

Physical evidence for D. simulans introgressions on 2L. (a) The PstI-digested PCR products at the Adh locus at the cytological position 35B2: Lane S, the C167.4 strain of D. simulans; lane I, an introgression subline (Int(2L)D+S/CyO); lanes M1-M3, D. melanogaster lines used in the crosses (M1, CyO/bw^VDe2; M2, Oregon-R; M3, C(1)M4, y²/In(1)AB, f). Lane I clearly exhibits the heterospecific pattern. All other five introgression sublines show a pattern identical with that of lane I. (b) The PCR products at the ex locus at the tip of 2L (21C3–4). DNA sources for each lane are identical with a. In total, four sublines carry this distal introgression. (c) Polytene chromosomes of the Oregon-R/Int(2L)D+S heterozygote. Note the asynapsis at the tip of 2L, which is always associated with heterospecific chromatids between D. melanogaster and D. simulans (35).