I apologize if this comment is far from the original topic of this thread. I am homozygous for the geek gene. A mutation that leads to a deletion (single base pair or larger) almost always leads to a loss of function mutant - a mutant plant for which the mutant gene is non-funtional. As DarJones points out there were several independent loss of function mutants in the gene for chlorophyll degeneration in the fruit, all leading to the retained chlorophyll (or black) phenotype. They are allelic - acting as the same allele for the gf gene. Based on the paper Lee references, PL is controlled by a transcription factor (regulatory gene) that controls expression of one or more functional genes (as is the gene controlling yellow vs clear epidermis - red vs pink). Transcription factors can control multiple genes in multiple pathways, thus the "pleiotropic" effects Dar references. Aft, controlling anthocyanin production in tomato fruit, is another interesting transcription factor - now understood to also influence delayed ripening. I also agree with Dar that a reversion mutation PL to RL is very unlikely.
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