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Hybrid Dysgenesis

A historical term for various genetic phenomena caused by transposable elements in Drosophila. It entails mutations and chromosomal rearrangements in hybrids of two genetic stocks. P-M system: The P-strains carry a transposable element and a suppressor of transposition. In the other strains (M), there is a genetic factor that derepresses the transposase and thus the hybrid becomes genetically unstable, while both the parental forms are stable. (The P and M originally indicate paternal and maternal conditions, respectively.). In Drosophila, over 30 different hybrid dysgenesis systems have been identified. The best known among them is the P-M system. The physical structure of a complete P element is shown in the diagram (see Fig. H80).
Figure H80. The structure of a complete P element of Drosophila (2,907) flanked in the genomic DNA target site by 8 bp direct repeats. The numbers in parenthesis indicate the nucleotide positions