Molecular Genetics

A complex genetic phenomenon, hybrid dysgenesis, led to the discovery of P transposable elements in Drosophila.

Facts

When Drosophila males of the P cytotype are crossed with females of the M cytotype, progeny exhibit a complex of abnormal traits (male sterility, frequent mutations, chromosome breaks and rearrangements, distorted segregation). The complex is called hybrid dysgenesis. Hybrid dysgenesis does not occur when the cross is reversed. P cytotype individuals contain 30 to 50 copies of a DNA sequence known as the P transposable element. In dysgenic individuals, copies of the element are found in new locations. There are autonomous and non-autonomous P elements. The autonomous P element encodes one transcript with four exons. It creates an 8 bp target site duplication on transposition.

Interpretations

• P elements are typical transposable elements , containing terminal inverted repeats and creating target site duplications on transposition. Autonomous P elements encode a protein which is probably the transposase.
• Hybrid dysgenesis results from activation of the transposition ability of dormant P elements.
• P elements are maintained in a dormant state by a factor present in P cytoplasm .
• Transposition causes a variety of genetic aberrations.

Further information

• In somatic cells, removal of the 5' most intron is prevented, so that a truncated protein, missing sequence encoded by the last exon, is produced P element pre-mRNA. The resulting truncated protein acts as a repressor of transposition. In germ cells, removal of the intron is allowed. The active transposase is made. This is an example of regulation by differential splice site suppression .

This is page 32217 of Molecular Genetics by Ulrich Melcher , © 1997, 1998, 2000-1, 2006