Biology Reference
In-Depth Information
Figure 9.5
Targeted gene mutation in
D. melanogaster
is based on the gap repair hypothesis. If a
P
element jumps out of a normal gene, it will leave a gap that must be repaired. Repair is thought to
involve using DNA with homologous ends from within the genome as a template for DNA repair.
If a new
P
element with a modified gene structure is present, the sequence in the gap can be filled
in using the modified gene as the template, leading to a targeted gene alteration. (Modified from
Gloor et al. 1991
.)
is sufficient to promote gap repair. However, gap repair was sensitive to single-
base mismatches within the homologous regions. Interestingly, the data sug-
gested that the ends of a broken chromosome could locate a single homologous
template anywhere in the genome using a short stretch of closely matching
sequence. How this occurs remains mysterious, but the search is sufficiently effi-
cient that up to several percent of the progeny exhibited targeted-gene replace-
ment at the
white
locus. This high rate of gene conversion is considered to be
