Positional information and morphogens

Here we go again — I said I’d try to make a youtube video about developmental biology every week, and I’m keeping that promise. I’m thinking, though, that my last couple of efforts were too big and indigestible, weighing in at 40 minutes each, so I’m going to try instead to present brief introductions to basic biology, and see if those are more interesting to people. I aimed for 10 minutes, but hit 12 instead — sorry, I’m a college professor, wind me up and let me go and I won’t shut up.

Let me know if this format is easier to stomach, and suggestions are welcome.


  1. jrkrideau says

    Looks okay to me but when I first saw the flag I thought you had take up President Macron’s offer and fled to France.

  2. golkarian says

    Are there really sinks? In 2d or 3d diffusion should be enough to dilute the signal (either 1/r or 1/r^2 respectively), wouldn’t it? But then the model wouldn’t work in 1d…

  3. damien75 says


    The sink model doesn’t work in 1D, except if you take into account the fact that the morphogen molecules are absorbed by the cells on the way to the sink. If the cells that bind the morphogen do not re-release the morphogen, if they digest it, so to say, then each cell acts as a sink.

    In that view, the sink on the side far to the flagpole is not necessary. Fewer and fewer morphogen molecules are going to make it to the locations farther and farther away from the flagpole.

    But I agree with you, in 1D, if the morphogen is not digested by the cells on its way to the sink, then its concentration should be the same across the flag.

  4. seachange says

    In pharyngula when you print a diagram, you put an explanation of what that diagram means under it or reproduce the explanation that comes with it.

    It was not at all clear what the elbow arrows meant in the flag diagram, and it was not at all clear what the t-ending of a line between two genes means differently from an arrow ending. When I was going to college I would sketch diagrams quickly and put some keyword next to it in my notes, nowadays I would take a picture with my phone, of course. But the reason I would do this is because it is hard for me to process the lecturewordsandbodylanguage for sonic information at the same time as the visual diagram information. What cna I say, my analytical brain is slow. Not all professors would stop and say what their diagrams meant. And you definitely don’t, until your are done and are about to turn the page and then it’s wtf time pick the needle up and drop it back a few minutes aha!

    You have an AOR (album oriented rock) time frame for your chunks of information that is to say whether or not you know you are doing this, you attempt to cram “an idea” in between three and four minutes. If you find yourself not fitting, you forget to breathe and your tone and inflection drop off as you speed up. In the forty minute videos this gets pretty pronounced as your run out of oxygen. Breathe! Take more time if you have to, but breath support comes first.

    Keep your hands away from your face please.

  5. jrkrideau says

    @ 8 Pierce Butler
    A French flag? That’s, that’s – UnAmerican!!!

    You’re right but the Dutch flag has horizontal stripes.

  6. damien75 says

    I have watched it again, and not everything is clear to me.
    I’ll start with just one question : does the word dorsal in the video mean at the same time two different things, being the name of a side of the embryo and the name of a gene ?