Of Mice and Men

My thoughts upon reading Endless Forms Most Beautiful, by Sean B. Carroll

Where should we look for the well laid plans that sculpt mice and men so differently? Well in the genome, of course, but there we meet a problem. Men and mice each have about the same number of genes, about 25,000. The conundrum gets worse. The genes are not only the same in number, but for most purposes they are the nearly the very same genes, producing very similar proteins.

The answer to this and many other puzzles of development, form, and evolution seems to be that it's in the switches that turn those genes on and off. If we think of the genes as the keys on an old fashioned player piano, the switches are the piano roll. It's the sequence of switching that orchestrates the notes into the symphony of development. For the most part, man and mouse are built out of the same cell types and tissues - different architectures built out of the same old Lego blocks.

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