A set of Drosophila melanogaster was generated,
all derived from a common isogenic base stock
and each with a single new P element insert on the
second or third chromosome. The lines were
scored for their body size, measured as thorax length. P
inserts were associated with highly
significant effects on body size, although the genotypes of the construct
and of the control
prevented deduction of the direction of mutant effects. In
addition to mutant effects on the thorax
length of both sexes, there were also highly significant sex-specific
effects. Pleiotropic effects of
inserts affecting body size on viability and bristle number, as
ascertained in a separate study of
these lines (Lyman et al., 1996), were weak. Insertional
mutagenesis is potentially a powerful tool
for investigating the genes involved in size-control in Drosophila,
but the technique requires fine
tuning for use on polygenic and fitness-related traits.