Re: is it possible to find enlarge an insect by a gene

The short answer? Yes, although how much larger an insect can be than 
normal and be healthy is a harder question.

The long answer:

I'll talk about fruit flies here, and how they control their size, because 
that's the model biologists usually use to study insect development.

In the fruit fly Drosophila, there are several well-known mutants that 
cause _decreased_ body size. For example, flies with the chico mutation 
are tiny - even for fruit flies, and that's saying something. Usually 
these mutations are in genes in the fly's version of the insulin signaling 
pathway. (Yes, the pathway that's involved in diabetes in humans.) So if 
you lose insulin pathway signaling, you get a smaller insect. And if you 
artificially increase it by making a fly express more insulin-like 
peptide, you get a big insect, as we see here:
 
http://www.molbio.princeton.edu/courses/mb427/2001/projects/03/endocrine.html#fig2


Now, that's not really a mutation, it's researchers tinkering with gene 
expression. But with that result in mind, we can ask what kind of mutation 
would give a bigger fly. Suppose some gene makes a protein that normally 
represses insulin signaling. If we mutate that gene, that repression 
should be stopped, and insulin signaling should be stronger, which should 
give bigger flies.

Sure enough, the gene Pten normally represses insulin signaling, and some 
mutations in Pten give us flies that are bigger - 50% heavier than normal. 
Now, this has been tested in fruit flies, but what's true in fruit flies 
is probably true in insects in general, and may even be true in people.

(Note: If you read through all of that and found it interesting, there may 
be a career in fly genetics waiting for you.)

Sources, if you're interested:

1. Christopher J. Potter and Tian Xu. Mechanisms of Size Control. Current 
Opinion in Genetics and Development. Volume 11, Issue 3. pp. 279-286. 
(2001). 

2. S Oldham et al. The Drosophila insulin/IGF receptor controls growth and 
size by modulating PtdInsP3 levels. Development 129, 4103-4109 (2002)

The second one's a bit technical. But the first one could probably be read 
and understood by a high school student with a good biology background. It 
might be behind a subscription wall, though. See if clicking on the "Full 
Text Article" button at this site will let you in:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?
cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11377964&query_hl=3