Reading the DNA of a single human cell

Eric Metaxas, Life, God, and Other Small Topics: Conversations from Socrates in the City (New York: Plume/Penguin, 2011) includes the transcript of a 3 December 2008 New York City speech (“The Language of God: A Believer Looks at the Human Genome”) by the physician and geneticist Francis S. Collins, M.D., Ph.D, who was, at the time, between his assignment as leader of the Human Genome Project and his subsequent appointment by President Barack Obama as the director of the National Institutes of Health, a position that he still holds today.  Here is a passage from that transcript:

So, what is the genome anyway?  The genome is made of DNA, and it really is an instruction book — that’s a pretty good metaphor. . . .

All of the DNA of an organism is its genome.  The information is encoded within a double helix for which Watson and Crick figured out the structure back in 1953, when I was three years old.  Basically, the way DNA carries information is by the series of chemical bases that are abbreviated A, C. G, and T.  It’s the order of those letters, those chemical bases, that carries out the information that then gets passed from parent to child down through the generations.

Suppose you had to guess, assuming you didn’t know the answer, how many of those letters of the instruction book it would take to specify the biological properties of a human being?  What number would you guess?  It can’t be infinite.  You have to have this information inside each cell of your body.  Every time the cell divides, it’s got to copy the whole thing; so, you wouldn’t want it to be larger than it had to be, at least, not by much.

The answer is about three billion.  Now, three billion is a big number.  Even in Washington, it’s a big number, although some might debate that.  It’s hard to think about that number and the fact that you have that inside each cell of your body.  If we decided right now, because this is a special evening and this is Socrates in the City, that we should read the human genome, what do you think?  Sure, we can do that.  I’ll start over here, and you can start reading A, C, G, T, T, G, C, T, and so on, and when you get tired, you can pass it to the next person and we’ll just keep going until we’re done.

You wouldn’t mind that, right?  That would be memorable.  But you might not survive, because for seven days a week, twenty-four hours a day, we would be at this task for thirty-one years, and then we’d finally be done.  You have that information inside each cell of your body, which is just a phenomenal thing to contemplate, and you got that from your parents.  (304-305)