> Gene's are letters in a story. To say "That's a salmon gene! It doesn't belong in my tomato!" is puzzling, like "That letter belongs to another book! Keep it out of this book!"

Using the same reasoning we could pick some pieces from an apple computer, mount it in a PC and expect that will fit in place and work flawlessly because, well... plastic is plastic. Right?.

It does not work like that. Organisms has been designed and polished for millions of years to work as a whole, all expensive useless stuff has been pruned for good reasons, and yes, this salmon gene -most probably- will not belong to a tomato... because is part of a salmon.