I am reading fw2.2: A Quantitative Trait Locus Key to the Evolution of Tomato Fruit Size (doi: 10.1126/science.289.5476.85).
The authors are trying to find the gene that makes tomatoes bigger. As far as I understand, previous research had narrowed it down to "something" in the region of the genome called fw2.2. They are trying to determine the actual genetic elements responsible (which turns out to be a gene similar to human HRAS).
Supposedly, the big-fruit allele is recessive and the small-fruit allele is dominant.
They say (in section Genetic complementation with fw2.2) that:
- They got a YAC containing the fw2.2.
- They "screened a cDNA library" with the YAC to find transcripts that were potentially relevant. (How?)
- They "screened a cosmid library" of genomic fragments to find the stretch of genome that the cosmid came from. (How?)
It is unclear to me how steps 2 and 3 work. Can someone explain how you can take a YAC, cDNA library and cosmid library to find the gene inside the region responsible for your trait, as these researchers describe?