The Illinois Long Term Selection Experiment

I wrote this in 2009 before we moved back to Georgia.  Reposting it because a student in my non-majors Cell Biology & Genetics class asked a whole bunch of questions about the experiment when I mentioned it this week:

Just wanted to put in a short entry on something I stumbled across many months ago. Its an experiment that has been running continuously since 1896 at the University of Illinois that might at first sound pretty boring.  Ok, for a lot of people this will be boring no matter how many times you read it;  I can’t help that I am a nerd.

1. Take ears of corn from several different corn plants
2. Dry kernels from each
3. Measure the % of oil and protein in each (by weight)
4. Select the plants in the top 20% for oil or protein content
5. Select the plants in the lowest 20% for oil or protein content
6. Start next generation using only selected plants

Repeat (for over 100 years)

This is whats called “artificial selection”, meaning basically that humans (and not the environment) are determining which organisms get to reproduce and pass their genes on to future generations. I will save my rant about how humans are perfectly natural and how, to my mind, there should be no distinction. The results of this experiment are complex and I don’t even pretend to understand most of it yet, but here is the outermost slice of the cake:

While “normal” corn kernels are 4% oil, 9% protein, 73% starch and 14 % other stuff, the corn selected for high oil content is now at 20% oil. These results have pretty important applications for an increasingly hungry planet. The corn selected for low oil content went down to 1.1% oil but that experiment had to be stopped as those plants had serious trouble reproducing. The protein content selection experiment showed equally dramatic changes.

I haven’t done so yet, but there seems to be a lot of good fodder (ah, theres a good pun) for teaching evolution, or at least giving a well studied example of the effects of artificial selection besides dog breeding. There are nice tie ins with metabolism (“why might plants with so little oil have trouble growing and reproducing?”), biochemistry, hypothesis construction, experimental design etc etc.

Speaking of hypothesis – this is the part that I want to understand better next: One prediction that was initially put forth was that the variability of oil content or protein content of the selected organisms would go down under such heavy selection pressure. Such a drop in variability would have meant that over time there was no “top or bottom 20%” to select. Given what we know about genetic variation and how it arises, it makes sense that such heavy selection (i.e. – reducing the variability) would quickly outpace the generation of “natural” variation in oil/protein content. But so far it hasn’t……there is something important there.


About SubOptimist

I am an Associate Professor in the Science Department at Georgia Perimeter College, Clarkston. I teach introductory biology courses at both the majors and non-majors level in addition to microbiology. Previous to that I spent 7 years as a postdoctoral researcher on different viruses. While I don't miss being on the "grant treadmill", I think better when I write and miss writing up data for papers and grants; this blog helps me with that a little. And sometimes my kids' insanely funny and cute antics need to be shared with the world. Any view expressed in this blog is that of me personally and not Georgia Perimeter College or the GPC Clarkston Science Department.
This entry was posted in Evolution, Uncategorized and tagged , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s