I came across a passage on enhancers that sounds out-of-whack to me:
...an enhancer sits on just one of DNA's two strands (usually the same strand as the protein-coding DNA gene itself). This is unlike a protein-coding DNA gene, which might need to be on both DNA strands——in a so-called homozygous state, in order to surface as a phenotype——like the classic case of blue eyes.
This is what makes no sense to me, since, AFAICT, whether something is in one or two strands has nothing to do with zygosity.
The authors continue:
And this is [an] evolutionary advantage: an organism doesn't have to wait for a change on both DNA strands. The bottom line is that evolutionary tinkering is in principle much easier with enhancers...
Is there a grain of truth in what the authors' write, despite their muddled explanation? IOW: does the fact that enhancers "sit on just one of DNA's two strands" somehow facilitate "evolutionary tinkering"?