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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