While I would rather wait for push to chime in to clarify that statement, I have other things I need to do tonight so I figure I’ll get the ball rolling as is.
CLIFFNOTES: it happens. We can observe it. We can test it.
We know that information can be added to the genome; this is a fact. And, we not only know that it DOES occur, we know various mechanisms behind WHY it occurs; e.g., as a result of unequal crossing over during meiosis I (“crossing over” refers to a point during cell division in which each pair of chromosomes swaps - or, crosses - genetic information with its counterpart to form a recombinant chromosome as a means of ensuring genetic diversity in offspring). When crossing over is unequal, the results can vary wildly - anything from a portion of a single gene to several genes can be found. In the event that introns (noncoding segments that nonetheless provide crucial functions) are transferred alongside the exons (coding regions), we now have a chromosome with extra material capable of expression. If not, there is still new information (albeit defective, noncoding, whatever) on the recombinant chromosome that presents a potential for further alteration down the line.
Another example would be in the case of transposable genetic elements, such as retrotransposons (which are copied to mRNA to cDNA and then inserted back into the genome) and DNA transposons (in which DNA segments are enzymatically jostled about without an RNA intermediate). The latter does not add anything “new” to the individual (it is simply a rearrangement), though that rearrangement can be passed on as “extra” information. The former, however, IS new information since the original sequence is copied and reinserted.
There are obviously other examples, the more obvious being cases of entire chromosome duplication (Down, Klinefelter’s, Edwards syndromes), but I think we get the picture.
So, we know that it occurs… but can we see/test/observe it? Yes, we can. If we chemically arrest cells during a particular stage in their division (colchicine or colcemid during metaphase is a textbook example, but I’m not a geneticist so I don’t know the latest-and-greatest), we can actually take the chromosomes, pair them together, stain them and lay them out for analysis. This is called karyotyping (and I’m sure if you Google an image of it you will recognize it even if the word itself in unfamiliar). Actually nowadays, our technology is so advanced we can use DNA probes specific for certain sequences to bind and fluoresce for us so we can see what’s going on (fluorescence in-situ hybridization technology, or FISH).
So, yeah. And I just wanna nip one particular objection in the bud straightaway: while many of these examples DO result in pathological states, this is not a universal rule. Not all mutations are bad. Please Google it or something before trying to argue otherwise.
