Once again Asimov is at his best, this time explaining DNA and the underlying genetic code in an easy to understand manner. He starts with the fundamentals of the language of chemistry, the symbols for the elements, diagrams of molecules and the basics of organic chemistry. Using this as the foundation, he then describes the structure of amino acids and how they combine to make proteins.
The next question is of course how cells "remember" the sequence of the amino acids in the proteins used to construct it. This requires a digression into the structure of DNA and the correspondence between the components of the DNA molecule and the protein molecule. Asimov also spends a great deal of time describing the historical record of the discoveries of how characteristics are transferred from a parent to their children. This is an excellent book for learning the fundamentals of these transfers.
The line that I found most interesting is the last paragraph of the introduction.
"This book is an attempt, then, to explain the background of the breakthrough; the full meaning of the breakthrough and its immediate consequences; and, finally, a forecast of what the breakthrough may bring about in the future - what the world of 2004 may be like, as seen through my own wishful eyes."
Now that the referenced year has arrived, how accurate was Asimov's vision? He is right on many things, accurately predicting the use of microorganisms to create proteins. However, he misses the single most significant event in genetics, the complete sequencing of the human genome.