"Interesting. Please elaborate. I remember reading something about this a year or so ago, but I've looked and there's not much information available. Thanks, MM"
Mapping genomes is just now giving us the raw data required for this proof/disproof.
Pick 3 sequentially "evolved" species with the same alleged common ancestor. The oldest species A has "gene 451." Species A supposedly branches into Species B, which has no trace of gene 451. Species B then purportedly branches into Species C, which *has* gene 451.
That would be code skipping, something beyond the ability of Common Descent to explain; it would falsify, conclusively, Evolutionary Theory (though no doubt the last holdouts of Darwinism will retreat to a viral defense to attempt to explain such code skipping)...
...On the other hand, we see code skipping in intelligently designed software all of the time. Re-using old code, even years later, is common, though numerous software programs written in between such re-uses of particular code won't always have such programming routines.
Code skipping is therefor common under ID, but ridiculous under ET. Genes that have disappeared in one species do not suddenly re-evolve back into a new child species.
This "problem" is merely an artifact of your model. You seem to assume that the species you call B at present is the same as it was as the first branching point and that it must have lost gene 451 between the first and the second branching point.
However, the more likely scenario is the one where species B still has gene 451 after branching off from species A and only loses it after splitting off from species C.
This confusion could be avoided if you used different labels after each branching point, i.e.:
Species A branches into species B and C. Later, species C branches into species D and E.
Today we observe that species B and E both have gene 451 but not species D. This may be explained by the fact that species C lost the gene but somehow species E magically regained it or which is more likely, that species C still had gene 451, inherited it to both D and E but later D lost it. (Of course there is also the scenario where species A didn't have this gene and B and E 'evolved' it independently of each other, but this is even more unlikely)