Site Redesign

Regular readers of HDWKI might notice that the site is undergoing a pretty extensive redesign at the moment.  I’m trying to make it easier to use, but various functionalities might blink on and off for a bit as I experiment with the new layout.  Please bear with me; it’ll all be over in a bit.

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Early example of a weather map, from 1888. Source: NOAA.

How do we know what tomorrow’s weather will be? (Part 2)

Last time, we looked at the agony and ecstasy of the life of Robert FitzRoy, the world’s first weather forecaster.  Like most other weather forecasters, FitzRoy provided an invaluable service, and yet was mocked resoundingly when his forecasts were in error.  Unlike most weather forecasters, this criticism drove him deeper into an already deep depression, and he ended up committing suicide only a few years into his new gig.  We may empathize with FitzRoy’s plight, but who among us hasn’t at some point been in awe of the sheer inaccuracy of a weather forecast?  Why should FitzRoy have it easier than Lady Catherine, Jane Austen’s archetypal ultrarich know-nothing?  Of course, this naturally leads us to the question:  will we ever be able to make a truly accurate weather forecast?  The answer to this question is a big fat no.  But the path to that big fat no is quite a bit more interesting than you might expect.

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Note the change in color from white to orange to red at the top of the candle flame.  The blue color at the bottom is caused not by blackbody radiation, but by a different process where electrons give off light by undergoing quantum jumps in energy. Source: Matthew Bowden www.digitallyrefreshing.com

How do we know that light is a particle?

If you’re reading this blog, you probably have a passing familiarity with the word “photon,” even if it’s only in reference to the torpedoes that arm most of the Federation ships on Star Trek.  But just in case you chose to spend your teenage years enjoying sunlight and people that exist in real life, a photon is the smallest possible particle of light that you can have.  “But Keith,” you say, “I thought you just said that light is a wave.  Now you’re telling me it’s a particle.  Most of your arguments in the last post about light had to do with showing how light can’t be a particle.  It can spread out, interfere with itself, bend around objects, remember?”  Yes, I remember.  I was hoping you wouldn’t notice.  I guess I’ll have to try to distract you by changing topics completely.  In a previous HDWKI, we discussed the Doppler effect as a way to find planets orbiting other stars.  In it, we mentioned briefly that blue light and red light have different energies, and that blue light is more energetic than red light.  Actually, it’s a long-established fact that the shorter the wavelength of light, the more energy the light contains.  And you’re probably asking right now:  “What does any of this have to do with light being a particle?  And, come to think of it, how do we know that shorter wavelengths of light are more energetic, anyway?”  I would tell you to stop asking questions faster than I can answer them, but in this case, the answers to the two questions are related in a pretty unexpected way.

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Reaction of two alanine molecules.  The peptide bond is highlighted in yellow.

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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Visual summary of Griffith's experiment.  Source: Madeleine Price Ball

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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EyeColors

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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Picture of 23 pairs of human chromosomes.  You might notice that the final pair doesn't look like a pair.  That's because it's the sex chromosomes:  one is an X chromosome and one is a Y chromosome, meaning the individual to whom these chromosomes belong is a male (female is XX, for the record).

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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Examining how we know what we know