Yes, it was addressed. Put simply, through analysis they identified the specific gene and the changes to the gene that provided the Swedish population with freeze tolerance, then they checked their analysis by inserting the Italian version of the gene into a Swedish population and observed that freeze tolerance was lost.
HBD's point was that these are the types of changes one would expect as different populations of the same species experience different mutations and different selection pressures.
In this case it must be natural selection, different versions showing up and the adapted one surviving, but nothing was said to prove it was a mutation.
Read much?
"So they sequenced this gene (named CBF-2) and found that the Italian population had a deletion of 13 nucleotides which resulted in a stop codon and a truncated protein (sound familiar?). When they inserted the Italian CBF-2 allele into a Swedish genetic background (all other loci were of Swedish origin except the Italian CBF-2 allele) the plant lost its freeze tolerance. SO we have a Swedish CBF-2 allele that helps the plant tolerate freezing temperatures and an Italian CBF-2 allele that does not have freezing tolerance."
A deletion of 13 nucleotides is a mutation.
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