The BioGeek Memoirs: Snapdragon

I just love snapdragons! I mean, they have those cute little faces; they do look a little like dragon faces if you use some imagination.

Snapdragons are great plants for me in my gardening efforts. They are really hardy, tolerate dry conditions, and there are new varieties that are small and easy to grow in containers and along the edge of your driveway or garden. The picture above is one that is growing in the margin between my rocked-in area and the driveway; I didn’t plant this guy; it is a volunteer that sprang up from a previous year’s plantings. The original plant was something like this one… a mixture of orange, yellow and pink that changes in the flowers as they age. Pretty cool, huh. I look at the plant and wonder how/why the pigment in the flower is changing over time. BioGeek, right?! It gets even better…

Do you see all of those colors? They are the result of genetic recombination that happened in the original plant’s flowers when the plant reproduced and created the seeds that rose up to produce this array of colors. Some of the offspring have clear-colored flowers (the yellow and the red), while other have the mixed hues and color-changing characteristics of the parent plant.

Notice, I said parent plant. The funky thing about snapdragons is that they self-pollinate and reproduce on their own with the pollen getting to the stamens within the closed flower without any intervention by outside helpers like wind or insects. In fact, they are so hard to open that only a really heavy insect like a bumblebee can open the flower to get to the nectar inside. As the (big old fat) bumblebee climbs into the flower the little hairs on its body pick up pollen. When the bumblebee flies on to another snapdragon and then climbs into that flower it can carry the pollen in with it to cross-pollinate the new plant with the previous one’s pollen.

Bumblebees started showing up in my garden last week, and I would like to believe that they have been busy with the snapdragons too. If you snap open one of the flowers like I did in the picture above, you can see the pollen-carrying anthers above the opening and then waaaay down at the bottom of the flower is the nectar with the ovary. An industrious bumblebee can push open the flower and then muscle its way in to the bottom. Yay! More flower colors are on the way when there is crossbreeding among my plants. Here’s a great blog posting (Ray Cannon’s Nature Notes) showing a bumblebee taking on a snapdragon.

All this brings me to Mendel and classic genetics. Gregor Mendel (1822-1884) was a monk who had a deep interest in the science. He lived in a time when genetics was very poorly understood, and the basic question was “how are traits transmitted to new generations?” Mendel chose a plant that self-pollinated like a snapdragon (pea plants) and controlled the cross-pollination between parent plants with distinctive characteristics like the color of the flower, the height of the plant, or the color of the pea. He cut away the pollen producing structures in the flowers, used little brushes to carry pollen from one plant to another (taking on the role of the bumblebee in snapdragons), and then put little fabric hats over the flowers to prevent any other pollination from occurring. Tedious, right? Anyway, this work led to the essential understanding in basic genetics that we all now know. Some genes are dominant, and others are recessive. You have two copies of each gene (one from your mom, one from your dad), and the inheritance of which copy you got from each parent is random. Here’s an online tutorial of classic genetics maintained by the Cold Spring Harbor Laboratory.

Good thing that Mendel didn’t choose snapdragons. Snapdragons are a problem for classic genetics because their genes don’t always follow the dominant/recessive inheritance pattern. Instead, some of the colors in snapdragons are both expressed at the same time, and we call that codominant. So…. a red snapdragon crossed with a white snapdragon will produce plants with pink flowers. We now understand how and why that happens, and there are lots of other examples of non-Mendelian genetics like blood type inheritance and tortoiseshell cats. If Mendel had chosen snapdragons to study, he would have floundered around forever, but thanks to him (and pea plants) the first understandings were worked out. Think of how hard that was… no one knew what the genetic material was or had glimpsed a chromosome, but he figured out the process using his pea plant data and some truly exhausting math. Way to go, Mendel!!

So, when I see my snapdragons, I am transported once again to my biology classroom and those early genetics lessons with students. I am connected to the world of science and the legacy given to me by Mendel and others. Why are my flowers a mixture of pink, yellow, and orange? Hmmm…. maybe there is more than one pigment gene at work at the same time, and the amount of pigment being produced is changed as the plant ages? Is this some funky combination of red and yellow genes? I kind of think so, since I now have plants with clear red and yellow flowers: they must have two copies of either the red or yellow gene. Is there another gene kicking in to modulate the amount of pigment produced as the flower ages? What about the pigments that I can’t see, but are there for the bees to see? This is so cool, and I just love snapdragons!!!!

This isn’t just a garden, but a genetics experiment that I’ve been running for a few years now.

Yay, science!