FIG. 4.

(A) Southern blot analysis of genomic DNA from mor-heterozygous flies with a Swi3D probe reveals an additional cross-hybridizing band in mor⁶. DNA was extracted from adult flies carrying different alleles of mor over the identical balancer chromosome, restricted with either EcoRI alone (left panel) or EcoRI plus HincII (right panel), and probed with sequences representing 3.6 kb of Swi3D cDNA. The lane marked mor⁷ represents a haploid amount of DNA derived solely from the balancer chromosome, and the lane marked P89B serves as a control since there are no alterations in the DNA derived from heterozygous P{lacW}89B flies in the sequences recognized by the mor probe. In both panels, the lane marked mor⁶ has a unique cross-hybridizing band (arrow) that is not observed in DNA derived from flies carrying other mor alleles, including mor⁵ (which was generated in the same genetic background as mor⁶). In addition, the intensity of the 2.3-kb band in DNA derived from heterozygous mor⁶ flies is reduced relative to that of the smaller fragments and is similar to the intensity of this band in DNA derived from the Df(3R)mor⁷ flies. Band sizes are shown at the side in kilobases. (B) PCR amplification of genomic DNA from a single wild-type (wt) or mor⁶-homozygous embryo, using a pair of oligonucleotides based on sequences within the 2.3-kb genomic EcoRI fragment of Swi3D. The anticipated size of the amplified fragment obtained by using this oligonucleotide pair (one starting at bp 1670 of Swi3D and the second beginning at bp 3570) is 2.0 kb (because of the presence of two introns of 62 and 64 bp). The actual size of the amplified fragment of mor⁶ DNA is about 1.7 kb. Molecular size marker positions are indicated at the left.