None of the above described has anything to do with environment.
That is only true because you left out the earlier step of how the cell knows that 'specific information is required'. This is often the result of signaling cascades initiated from the extracellular environment and can be affected by the larger environment of the organism.
Environmental effects are less obvious in humans because the womb is a very protective environment. In other organisms there are many clear examples of the effect of environmental factors, such as temperature effects on the sex of reptiles and the high sensitivity of amphibian development to salt and pH levels as well as water pollutants.
But DNA is the one and only source of genetic information.
This is obviously true because in terms of modern biology it is a tautology, what isn't true is that DNA is the only source of developmental information.
The other confounding factor is that in most larger organisms development is a highly stochastic process dependent on dynamic levels of proteins, especially those involved in signaling and transcription factors. So even with identical genetics and environment you can get a different phenotype in many instances just through chance variations during the developmental process.
I would say DNA is 99% responsible for any organisms physical state
I don't disagree with your general point about the importance of genetics but I think your 99% value is too high. Except in very controlled experimental situations the actual proportions of such things are very hard to measure.
TTFN,
WK
P.S. Just to be picky, if you are talking about
mRNA then the bases are adenine, guanine, cytosine and uracil.