First wet lab work I've done in more than a month. Also how often do you see a bottle actually LABELLED as "Strawberry DNA extraction"?

It’s actually quite easy* to extract visible quantities of DNA from fruits and vegetables using nothing less common than dish soap and rubbing alcohol. For our class we chose strawberries, but I also heard of people using kiwis and bananas to great success.

Of course it takes a mere second for someone to say “I don’t eat food with genes in it” and 15 minutes to prove them wrong by extracting DNA from an (organically grown) banana, but that imbalance between the time and effort it takes to repeat piece of false information and the time it takes to refute that same misinformation isn’t going to change. It is something anyone in the habit of going up against misconceptions with nothing but demonstrable facts on their side has to get used to.

The demonstration itself went pretty smoothly. Unfortunately, since it’s a hundred student lecture, we had to do most of the preparation beforehand, so I don’t think most of them realized just how easy DNA extractions can be.

*Note that this recipe calls for the use of meat tenderizer to break down some of the remaining proteins in the solution before extracting DNA, and points out that pineapple juice will make an acceptable alternative (as it also contains enzymes that break down proteins.) I mention this only to reiterate my point, as if you hadn’t heard it before, that pineapples are one of the most awesome fruits known to mankind.

Arabidopsis that carries broken copies of both the AP1 (apetala1) and CAL (cauliflower) genes. The flower bearing stems have been replaced by these cauliflower-head-like growths. Image from "Genome-Wide Analysis of Gene Expression during Early Arabidopsis Flower Development" by Frank Wellmer et al (in PLOS Genetics a creative commons licensed journal). Article here: http://dx.doi.org/doi:10.1371/journal.pgen.0020117

Just in time for me to put together my worksheet for Thursday! I’ve managed to work in the CAL gene, which I talked about last week in my discussion of Cruciferous vegetables:

Cauliflower plants (and broccoflower plants) have broken copies of the CAL gene, which (when it isn’t broken) is helps the plant decide to switch from producing stems that were bear flowers to the flowers themselves. Without a functional version of CAL, cauliflowers just keep making denser and denser stems, producing the distinctive heads of cauliflower. If you have journal access, you can read more about the CAL gene at this science paper: http://dx.doi.org/10.1126/science.7824951

I also threw in a question that uses the shrunken2 gene (one of the two most common genes that convert normal starchy corn into sweet corn). From the question in question:

Note the shriveling of the yellow kernels that carry two broken copies of the shrunken2 gene, the purple kernels carry either one broken and one working copy of shrunken2, or two working copies. The change in color is controlled by another gene nearby on the same chromosome, shrunken2 itself has no effect on the color of corn kernels. Photo credit goes to MG Neuffer and MaizeGDB.

Corn kernels without a working copy of the shrunken2 gene can’t convert very much of the sugar provided by photosynthesis in the leaves of the corn plant into starch. Instead, sugar itself accumulates in the kernel making the corn taste quite sweet.

When sugary corn kernels are dried, they shrivel up, while starchy ones remain relatively round and smooth. This has to do with the fact that sugars are water soluble while starch is not. So, as I understand it, corn kernels with more sugar are also a greater percentage water than corn kernels that are made mostly of starch.

The mutant form of shrunken2 was identified by John Laughnan, a maize geneticist at the University of Illinois Urbana-Champaign. The story of the discovery as told in Maize Genetics and Breeding in the 20th Century by Peter Peterson and Angelo Bianchi:

According to historical sources [E.H.C.] [This is Edward H. Coe], serendipity played a part in a practical discovery (1953) from which many sweet corn worshipers now benefit. Soaking and chewing upon a corn seed to aid in concentration is a pervasive but minor indiscretion in the profession, generally conducted surreptitiously and especially embraced when seeking rare mutations or recombinants. Muttering, so it is said, “that’s shrunken, too,” and “super, it’s sweet!” [John Laughnan] came upon the now popular and widely grown, high-sugar Super Sweet type. When next the reader has a table ear with butter (or better, corn oil margarine) and salt, it might be gratefully remembered that the sh2 factor is so close to A1 that it was originally attractive as a marker in intensive genetic analysis-else it might yet be only a phenotypic curiosity.

One of the things that sucks about moving into the area of comparative grass genomics is losing of the feeling of following in the footsteps of generations of maize geneticists. The maize community has, for lack of a better word, a sense of history.

A recreated example (should be familiar to anyone who, like me, took the first two weeks of intro botany):

The basic diagram of four parts of a (eudicot) flower. From the outside in. A: Sepals, small, generally boring green bits that look a fair bit like tiny petals. B. Petals. C. Anthers. The male part of the flower, responsible for producing pollen. D. Carpal(s) The female part of the flower. Pollen lands on the top surface, then grows a tube down into the flower to fertilize the eggs and central cells.

I’ve seen variants of this figure in 3 courses I took as an undergraduate, and now I’m using it myself. I’d be interested to hear if anyone has seen (or can think up) variants that might be easier for people with no background studying plants to grasp.

I can remember what finally got me excited about learning the parts of the flower, but it isn’t any help in trying to get these students excited about plants.  I got hooked when I first learned about the ABC model of floral development, and how breaking different genes can, for example: transform the sepals into carpals and the petals into anthers (class A), turn the petals into sepals and the anthers into carpals (class B genes) or create flowers than never produce reproductive organs just some sepals and then lots and lots of petals (class C genes). The story of the ABC model, which I should really write up sometime ::adding it to my long list::, is a discrete and engaging story of how science works, but I don’t have enough freedom in the order I’m teaching material to devote the time to telling that story when I’m supposed to be just teaching parts of the flower. And even if I had the time, throwing gene names and mutant phenotypes at people who probably haven’t taken any biology since high school seems more likely to scare students off then get them hooked on plant biology.