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 4)

When we last left off, we were feeling a little bummed.  Gregor Mendel never received the recognition he deserved for discovering the basic laws of heredity, at least not while he was alive.  August Weismann was struggling against criticisms of his theory, which said that inheritance passed from parent to child solely through gametic cells in a process known as fertilization that was essentially meiosis in reverse.  And it was clear that had Weismann (or anyone else, for that matter) just known about Mendel’s work, the burgeoning field of genetics would be poised to take a giant leap forward.  Why’s that?  Because Weismann and others had observed that, during fertilization, chromosomes come together from both parents in a way that was very similar to Mendel’s theoretical explanation of how heredity in pea plants worked.  Mendel lacked the intimate knowledge of chromosomes that Weismann had, but Weismann lacked the knowledge of heredity that Mendel had.  Once the two pieces of the puzzle were put together, it would be clear:  the inheritance of genetic traits from one generation to the next is determined solely by the chromosomes that interact when a sperm and an egg unite.

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How do we know the genetic code? (Part 3)

Last time, we explored the work of Friedrich Miescher and his discovery of DNA, but we didn’t talk about how DNA stores information about the traits we display and inherit.  That’s because at first no one had any idea that DNA was really all that important.  People just assumed it was yet another cellular substance in a deluge of substances being discovered during that period.  However, at roughly the same time that Miescher was doing his work, other scientists were finding new ways to observe never before seen structures and processes in cells.  But it was a long time before anyone suspected that these cellular observations were related to DNA.  This is a recurring theme in science:  researchers in different fields find themselves studying different aspects of the same phenomenon, and it often takes decades for scientists to put all the pieces together to give an accurate context for all of their data.

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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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How do we know the genetic code? (Part 1)

Over the course of the next few posts, I hope to tell you the story behind one of the most important codebreaking efforts in history.  The code at the center of this story does not concern itself with assassination conspiracies or terrorist plots.  There is no political intrigue or corporate espionage.  No couriers are relieved of their parcels (or their lives) during a clandestine midnight ride.  The code of which I speak isn’t really much of a code at all; its message can be read in the very faces of those who carry it.  And every single one of us, and everyone we know or have ever known or will ever know, carries this code with us.

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How do we know that diamond and graphite are different structures of carbon?

In the first part of this post, I explained how scientists found out in the late 18th century that diamond, graphite, and charcoal were all made of carbon.  As a quick explanation of how such different materials could be made of the same element, I put up the following photo, showing that diamond and graphite actually have vastly different structures:

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How do we know the brain is where thoughts occur?

Anyone with a brain knows that our thoughts happen in our brains.  But our metaphors belie our confidence in this assertion:  “I know it in my heart,” “I have a gut feeling about it,” “I use my muscle memory to play this game.”  Each of these statements says a little bit about what it feels like to process information.  Do we know that our thoughts occur inside our heads because we can feel them happening there?  Or do we feel them happening there because we’ve been taught very early on that our brains are where our thinking happens?

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