Monday, 4 January 2010

Virtual Plant Breeding Project

KorganIconThis blog is about my virtual plant breeding program. If you don’t know about Mendelian genetics, read my previous blog which explains the basics in an easy-to-read way.

The last frame of the animation on my previous blog is very interesting. It summarises all six rules of Mendelian genetics. This illustration explains why a child may have red hair even though its parents don’t but its grandmother does, it explains how hybrid seeds are made and why garden centres make money from selling F1 seeds, and it explains how to make a true-breeding plant from a hybrid.

Let’s say I breed together a red and a white plant and I get a bunch of hybrids. If I produce thousands of children from these hybrids, then I know I will get roughly 25% homozygous dominant plants, 25% homozygous recessive plants, and 50% heterozygous plants. So in this case, the majority of plants are heterozygous. But what if I make another generation from this one? What will the proportions of the second generation be? This was the question I had. What is the proportion on the 1,000th generation? And the 10,000th generation?

So I wrote a program that simulates this. Then it spits out the figures and I graph it and see the results. I took two heterozygous plants and made 1,000 children from them. Then, I made a 2nd generation by randomly mating members of the 1st generation. I did this for the 3rd generation, the 4th and so on. I simulated up to 10,000 generations. I recorded the proportion of homozygous dominants, homozygous recessives and heterozygous plants in each generation and plotted the results.

Here is a sample of the graphs. (click on them for larger image) In these examples, homozygous dominant eventually overthrows the others:

Well, does that always happen? Nope. Sometimes homozygous recessive won, as shown here:

So far, I've figured that the meek MIGHT inherit the Earth. But it's not certain. So I repeated this entire experiment 500 times. The figures settle down at around 50% each way. That is, out of the 500 experiments, homozygous dominant plants took over in 48.1% of cases, homozygous recessive plants in 51.9% of cases. Hybrids can never win.

I haven't included mutations or competition or any other environmental factors in these simulations. So what?

I've learned some useful things in all this. Maybe you read this stuff and use it.


  1. dude, you have no idea.
    this is the kind of stuff I want to do with my life! breeding and cross breeding trees and plants, and growing them!

  2. Man. All I have are questions!! I will only bother you with a few though.
    Certain plants do not appear to make offspring in the form of seeds. Is there a method to force a plant to produce seeds?
    I've had a few that I've never seen produce even one seed. I know they have to, because they ARE plants after all, but I just can't figure out how to get them to make babies. I'm absolutely horrible at producing living cuttings for some reason. I'm working on it though.
    I've planted a few of the seeds you sent me and nothing has grown yet, but it's definitely my fault, not the seeds. I only planted a few and being away from home often during this heat doesn't lend itself to plant watering enough.

  3. @Crysstian:

    I can only think of one example of a plant that does not produce seeds: seedless grapes. The only solution I can think of (that doesn't require a laboratory) is to breed your seedless male with a seeding female. Otherwise, you can still take cuttings of the plant.

    If your plants aren't producing seeds for other reasons, it might be that they're simply not getting fertilised thoroughly. Some species can be tricky about this and some require the interaction of insects by default.

    Definitely give cuttings a go. It's easy once you know the basics and the best way to preserve the traits of your favourite plants.

    In fact, I should probably write about how to do this in my next blog.

    Hey, it only took me a year to respond!