How do we know the genetic code? (Part 6)

In the previous post in our series on the genetic code, we chronicled the adventures of a number of chemists, biologists, and even an epidemiologist as they battled their way to a fundamental truth about genes.  Spoiler alert for those who haven’t read it yet:  genes are made of DNA.  It seems like such a basic fact now; most middle-schoolers can recite it.  But keep in mind that nearly a century separates Friedrich Miescher’s discovery of DNA from the widespread acceptance of DNA as the genetic material.

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How do we know the genetic code? (Part 5)

In the previous post of this series, we figured out that chromosomes carry genes, and we used genetic linkage and crossing over to start making gene maps of chromosomes.  Given enough data on offspring and inherited traits, we could continue this project and make ever more accurate gene maps, identifying the components of chromosomes in ever finer detail.  In fact, that’s what went on for some time after Sturtevant’s work in 1913.  But we know that this can’t be the end of the story.  We know what a gene is now, but we still haven’t talked about a genetic code.  How do genes even work?  In part 1, we introduced the concept that a gene on a chromosome can ultimately, through a chain of biochemical events, lead to someone having blue eyes:

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How do we know the genetic code? (Part 2)

In part 1, we looked at how DNA in our cells can cause cascades of effects that eventually show up as observable traits, like hair color or sickle cell anemia.  As an example, we looked at how a specific group of letters in some people’s DNA can lead, through a series of steps, to those people having blue eyes:

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