What words mean "not located yet"?

In the specific example you give (where presumably people have been trying to find the exact location, but thus far without luck), I would suggest elusive.

It does not generally mean ‘not yet located’, of course, but it can be used to mean it in the right context—and I'd say that's exactly what you have here.

yet to be discovered/identified/found

In Caucasians, mutations in a gene called CARD15 make a person susceptible to Crohn's disease, but Japanese with Crohn's disease have none of these mutations. Presumably a different gene, yet to be found, contributes to Crohn's in Japanese.

unidentified, undiscovered, unnamed

...provided validation that the unnamed feeling was an Autonomous Sensory Meridian Response ...

Edited in light of new information ("as in if you know something exists, but have not yet found the boundaries where it exists...don't know the chromosome or area...)

desired

...restriction enzymes are used to cut the desired gene out of the DNA in which it is found.

The lower the number, the higher the chance that the desired gene will be expressed poorly.

.....cells, regulating the lengths of DNA fragments, finding a desired gene

...establish the function of the desired gene. ...the desired gene in a plastid... ...removed and replaced with the desired gene... ...enough offspring express the desired gene to make... ...the gene probe can only become attached to the desired gene.

I think the word undiscovered fits the bill. Alternatively you might be after a word like theoretical or suspected.

Apparently, the term unplaced sequence already exists among the Genome Research Consortium, meaning:

A sequence found in an assembly that is not associated with any chromosome.

Alternatively, if the location is known only down to the chromosome, unlocalized sequence is used:

A sequence found in an assembly that is associated with a specific chromosome but cannot be ordered or oriented on that chromosome.

Is there any reason that a gene that is known (or suspected) to exist, but where its genomic location has not been determined, should not be referred to as unplaced or unlocalized?