A reader writes to offer (not a joke) information about a most revealing experiment, with respect to what DNA can and can’t do: Researchers implanted human embryonic neuronal cells into a mouse embryo. Mouse and human neurons have distinct morphologies (shapes). Because the human neurons feature human DNA, they should be easy to identify.
Which raises a question: Would the human neurons implanted in developing mouse brain have a mouse or a human morphology?
Well, the answer is, the human neurons had a mouse morphology. They could be distinguished from the mouse ones only by their human genetic markers.
If DNA really ruled, we would expect a human morphology. (Abstract follows.)
Meanwhile, can someone get hold of that guy, Walter Gilbert? Remember this?:
As geneticist Walter Gilbert put it, understanding our genetic composition is the ultimate answer to the commandment “know thyself.” Gilbert introduces his lectures on gene sequencing by pulling a compact disk from his pocket and announcing to his audience, “This is you.”* More.
Like, he should hear this stuff. Also, whither the selfish gene?
Abstract Human embryonic stem cells are pluripotent entities, theoretically capable of generating a whole-body spectrum of distinct cell types. However, differentiation of these cells has been observed only in culture or during teratoma formation. Our results show that human embryonic stem cells implanted in the brain ventricles of embryonic mice can differentiate into functional neural lineages and generate mature, active human neurons that successfully integrate into the adult mouse forebrain. Moreover, this study reveals the conservation and recognition of common signals for neural differentiation throughout mammalian evolution. The chimeric model will permit the study of human neural development in a live environment, paving the way for the generation of new models of human neurodegenerative and psychiatric diseases. The model also has the potential to speed up the screening process for therapeutic drugs. (full text follows – Alysson R. Muotri, Development of functional human embryonic stem cell-derived neurons in mouse brain, 18644–18648, doi: 10.1073/pnas.0509315102)
Jonathan Wells: Far from being all-powerful, DNA does not wholly determine biological form (Mutate a fruit fly embryo in every possible way, and observe only three possible outcomes: a normal fruit fly, a defective fruit fly, or a dead fruit fly.)
Jonathan Wells: We are far from a good theoretical model of organisms’ development (We are far from having a complete list of the components, as a matter of fact.)
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