Guided Inquiry: Genotype, Environment, and Selection
Week 1: Set-up Required readings: OpenStax Biology, Section 18.1 and Chapter 19 Objectives:
• Use the terms genotype, phenotype, variation, and selection appropriately. • Conduct a guided inquiry experiment to observe and measure the combined influence of
different genotypes and different environments on the phenotype of an organism. • Collect and manage data in excel spreadsheets. • Use statistical and graphical analyses to address a scientific question. • Write a scientific report based on data from a guided inquiry exercise, drawing on at least
five primary research articles, with complete and correctly formatted citations, including abstract, introduction, methods, results, discussion, and references sections.
Overview In this guided inquiry activity, you and your classmates will observe and measure the combined influences of different genotypes and different environments on the phenotype of an organism.
You will be using a special variety of Brassica rapa (pictured above) that was developed and bred by researchers at the University of Wisconsin-Madison to have a very short life cycle – it can go from seed (which you will plant in soil) to seed (which you will harvest from the mature plants) in around six or seven weeks. “Wisconsin Fast Plant” is the trademarked name of this variety of Brassica rapa.
How many other varieties of Brassica rapa are there? Do any of them have familiar common names? How long does it typically take for other varieties of Brassica rapa to go from seed to seed? Look it up!
Should we call the different types of Brassica rapa “varieties” or “sub-species”? What do you think?
This guided inquiry activity will take place over seven to eight weeks starting in the first week of labs in BIOL 1204. Over the course of the activity you will plant the Brassica rapa seeds, monitor the growth and development of the plants (e.g. production of flowers), make sure they get pollinated, harvest the plants and seeds, and analyze the effects of different environments and different genotypes on the growth and seed production of the plants.
Start a lab notebook, and write down answers or thoughts in response to the text in grey boxes. These might be useful in your final write-up!
To create different environments, we will be treating the plants with two different water regimes. In one regime, the plants will get all the water they need – in botanical and horticultural circles, this is referred to as “field condition”, and we will refer to this as the field treatment. In the other regime, the plants will be stressed by limiting their water supply – we will refer to this as the drought treatment. In essence, what we are doing here is simulating two environments: a wet environment and a dry environment.
Which will grow more and produce more seed – the plants in the field treatment or the plants in the drought treatment? What do you think? Actually, you can look up the expected effects of drought on plant growth and seed production!
In each environment (i.e. wet and dry), we will be planting two genotypes. It is possible to purchase many different genotypes from the people who own the Wisconsin Fast Plant trademark. We (your trustworthy and expert guides through this scientific inquiry – the BIOL 1204 team of instructors) have selected two genotypes for you to use in this experiment: The “standard” genotype and the “petite” genotype.
What’s the difference between these two genotypes? What is the genetic basis of this difference? Look it up!
How will these two genotypes respond to being grown in the two different environments? Will they respond differently? Exactly! Now you’re asking a scientific question! I guess we’ll have to do the experiment to find out!
If one genotype grows larger and produces more seeds than the other genotype, then one of the genotypes has a selective advantage over the other genotype. If this advantage persists over several generations (i.e. if the effect of the environment remains constant), we would expect the selectively favoured genotype to outcompete the other genotype. The selectively favoured genotype would leave behind more offspring, which would in turn leave behind more offspring, until eventually the favoured genotype completely eliminates the disfavoured genotype. Although we will only be observing these plants for one generation, the results of our experiment will allow us to predict what will happen over several generations (if the effect of the environment remains constant). We can hypothesize several outcomes of this experiment (see figure 1 for a graphical representation of these hypotheses):
A. the standard genotype does better than the petite genotype in both environments, B. the petite genotype does better than the standard genotype in both environments, C. the standard genotype does better in the field treatment, and the petite genotype does
better in the drought treatment, or D. the petite genotype does better in the field treatment, and the standard genotype does
better in the drought treatment.
Figure 1. A graphical representation of four possible outcomes of the effects of genotype (standard or petite) and environment (drought or field treatment) on the seed production of Brassica rapa.
Can you hypothesize other possible outcomes? How would you draw them on a figure similar to Figure 1?
What difference(s) between the petite and standard genotypes might have an effect on their ability (or inability) to tolerate drought? Can you make a prediction about the outcome of this experiment? Do scientists do literature searches before they conduct their experiments? You bet we do!
Are all the petite plants going to grow exactly the same amount and produce exactly the same amount of seed? How about the standard genotype – will they all be identical? Hint: probably not! There will be variation among individual plants! How much variation? This is getting complicated… We’ll probably need to do some statistical analyses! Fun!