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In-Depth Information
This chapter describes P elements and hybrid dysgenesis, and the methods
used in introducing P -element vectors into the germ line of D. melanogaster . This
approach to germ-line transformation inspired entomologists to attempt to engi-
neer insects other than Drosophila using TE vectors with a broader host range.
An analysis of the spread of P elements into natural populations of D. melano-
gaster previously lacking these TEs allows us to learn more about the evolution of P
and other TEs. Because TEs have been proposed as possible “drive mechanisms” for
the genetic modification of wild insect populations, the study of P -element invasion
into D. melanogaster may serve as a model to understand the potential for using
this type of drive mechanism for other insects. Analyses of P -element invasions also
may provide clues to the evolution of resistance (suppressive factors) to TEs.
Finally, several new tools have been developed that allow genetic modifi-
cation of Drosophila and other insects (see Section 9.19). These methods may
result in higher rates of transformation, increased stability and more effective
levels of gene expression.
9.3 P Elements and Hybrid Dysgenesis
Intact P elements are 2907bp long and encode a single polypeptide that has
transposase activity ( Figure 9.1 ). There are four exons (numbered from 0 to 3)
flanked by inverted repeats that are 31 bp long. The presence of intact inverted
repeats is required if the P element is to transpose (move).
Multiple copies of P (30-60) are dispersed throughout the genome of P strains
of D. melanogaster , but their activity is suppressed by multiple mechanisms.
Many P elements in D. melanogaster , and other Drosophila species, have some
sequences deleted, which makes them incapable of transposing.
Figure 9.1 Structure of an intact P element. There are four exons (0-3), separated by short introns
(thin line). The 31-bp inverted terminal repeats (sequences 1-31 and 2877-2907) are indicated by
the filled arrows. There are also inverted repeats at sequences 126-136 and 2763-2773. (Modified
from Engels 1989 .)
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