Lab Instructions_ Genetics and Evolution Act I Mission Memo

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Arizona State University *

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182

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Chemistry

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Apr 3, 2024

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Lab Instructions: Genetics and Evolution Act I Mission Memo Greetings Fellow Explorer: The decimation of the sunstalk forest has left many of Sarcannus' creatures without food or shelter. Your careful investigation of the environment points to a likely cause: metal poisoning. Fortunately, we discovered a few healthy sunstalks growing in the contaminated region. These survivors could be the key to saving this endangered ecosystem. If we confirm that heavy metals have contaminated the soil, we should conduct an experiment to determine whether the metal tolerance of the surviving sunstalks stems can be passed to their offspring. We need to work quickly to restore the sunstalk”: ● Do concentrations of heavy metals in the soil of the Sarcannian forest exceed the limit for healthy life? ● How should we design a breeding experiment to determine the genetic basis of metal tolerance? ● What phenotypes should we observe among offspring if metal tolerance depends on a dominant, recessive, or incompletely dominant allele? Universally in your debt, The AI Page 1

Appendix 1 Does the concentration of cadmium in the Sarcannian water exceed the limit for healthy life? We cannot ignore the overlap between the areas where sunstalks have died and the position of water pipes in the Sarcannian forest. This observation suggests that heavy metals from the pipes might have contributed to the death of the sunstalks. At high concentrations, heavy metals can kill an organism in several ways. For example, many heavy metals bind to proteins in cells and prevent these proteins from functioning. Other heavy metals trigger a natural process of cell death, called apoptosis. An artificial environment such as the Intergalactic Wildlife Sanctuary could contain elevated levels of heavy metals. In fact, heavy metals make up a fraction of the elements found in the structural framework of the sanctuary. Given the corrosion that we observed on the water pipes, we might expect that certain heavy metals have accumulated in the water used by the sunstalks in Sarcannus. The Intergalactic Wildlife Federation (IWF) follows the health and safety recommendations of the Galactic Environmental Treaty, which limits the concentrations of potentially harmful chemicals. This treaty specifies that no heavy metal should exceed a concentration of 100 parts per million (ppm) in water, which equals 100 mg of metal per liter of water (mg L -1 ). Any concentration greater than this limit could harm an organism such as a sunstalk. One heavy metal we know can be particularly dangerous to life is called cadmium (abbreviated in your periodic table as Cd). On Earth, cadmium has a variety of uses, including being used to make certain batteries and solar cells. My archives show that cadmium is one of several heavy metals present in the infrastructure throughout the sanctuary - so it certainly has the potential to be present in the Sarcannian groundwater. Your samples of water from the Sarcannian forest will enable us to determine whether any type of heavy metal exceeds the recommended limit for life. We’ll focus our initial analysis on cadmium given we know how dangerous it can be to life. We will follow three steps to answer the question “Does the concentration of cadmium in the Sarcannian forest water exceed the limit for healthy life?” Page 2

Step 1: Anticipate your analysis. Determine what you should observe if the concentrations of cadmium in water samples exceed the recommended limit. This step will help us identify the evidence needed to build an argument in Step 3. Step 2: Calculate the probability that the concentration of cadmium in water exceeds the recommended limit of 100 mg L -1 . Determine whether the concentration of cadmium in water likely exceeds the recommended limit. This step gives us the evidence needed to build an argument in Step 3, when we will conclude if an elevated concentration of cadmium in water could explain the widespread death of sunstalks. Step 3: Weigh the evidence and conclude if an elevated concentration of cadmium in water could explain the widespread death of sunstalks. Construct an argument to answer the question “Could an elevated concentration of cadmium have caused the widespread death of sunstalks in the Sarcannian forest?” Your argument should draw on your calculations in Steps 1 and 2. Step 1: Anticipate your analysis. To construct a sound argument, one must anticipate the evidence needed to support a claim. In this assignment, you can choose between two claims: Potential Claim 1: Yes, the concentration of cadmium exceeds the limit for healthy life. Potential Claim 2: No, the concentration of cadmium does not exceed the limit for healthy life. Directions : For question 1, evaluate each of the three figures in the question below and determine which one would support the claim “Yes, the concentration of cadmium exceeds the limit for healthy life.” 1. The answer choices below show the normal probability distribution that best represents the frequency distribution of the concentration of cadmium (mg L -1 ) in 20 samples taken from three different locations. In each figure, the y-axis represents the probability of observing a concentration of cadmium less than the corresponding concentration of cadmium on the x-axis. The x-axis represents the concentration of cadmium (mg L -1 ), with higher values indicating more cadmium Page 3

per liter of water. The dashed line indicates the recommended limit of cadmium, 100 mg L -1 . Select the distribution that best illustrates what one should expect to observe if the concentration of cadmium in a given location exceeds the recommended limit of 100 mg L -1 . A. Location A B. Location B C. Location C Step 2: Calculate the probability that the concentration of cadmium in water exceeds the recommended limit of 100 mg L -1 . To determine whether the sunstalks have suffered from cadmium poisoning, we need to determine whether the concentration of cadmium exceeds the recommended limit of 100 mg L -1 . In other words, we must use our water samples to estimate the probability that the concentration of cadmium exceeds 100 mg L -1 . Probabilities are usually calculated from a model of a probability distribution, such as the normal probability distribution (Figure 1). Before we use a normal probability distribution to calculate a probability, we should decide whether this probability distribution adequately describes the frequency distribution of our data. If not, we should use the data to calculate the probability instead of using a normal probability distribution. Page 4

Figure 1. Example of a normal distribution. The black line shows the normal probability distribution that best describes the data. This distribution, often called a bell curve, has a single, central mode and a symmetrical tail on each side. The mode is the most probable value. We will ultimately examine the concentrations of five types of heavy metals, but let's start with cadmium first. Using the link in Canvas, download the Excel file containing the concentrations of cadmium in water samples collected from the Sarcannian forest (sample size = 20). Then, examine a frequency distribution of these data. Using the frequency distribution, decide whether the data can be modeled with a normal probability distribution. We need to be sure the data meet the assumptions of this model before using it to draw conclusions. Directions: For questions 2 – 4, download the Excel file “Data: Concentration of Heavy Metals” in Canvas containing the concentrations of cadmium in water collected from the soil in the sunstalk forest (sample size = 20 water samples). Use Excel for calculations, modeling, and graphing. 2. Create a plot of a frequency distribution (also known as a histogram) of the concentration of cadmium in water (sample size = 20 water samples). Your plot should follow the formatting guidelines listed below. Page 5

Formatting Instructions ● Chart type: Column ● Y-axes title: “Frequency”; Font size = 18 ● Y-axis numbers: Font size = 14 ● X-axis title: “Concentration of cadmium (mg L -1 )”; Font size = 18 ● X-axis numbers: Font size = 14 ● Bins = Use the following 12 bins: 80 to 120, 120 to 160, 160 to 200, 200 to 240, 240 to 280, 280 to 320, 320 to 360, 360 to 400, 400 to 440, 440 to 480, 480 to 520, 520+ 3. Based on the frequency distribution, does a normal probability distribution reasonably model the concentration of cadmium in water? Yes it is a normal probability distribution that can reasonably model the concentration of the cadmium in the water. 4. Explain your answer to the previous question. Be sure to discuss the assumptions of a normal probability distribution and why, based on the frequency distribution, these assumptions seem appropriate (or not) for modeling the concentration of cadmium in water. Distribution has a peak and the data is not distributed equally around the peak, the chart looks like a bell graph which identifies a normal probability distribution. Now that we have determined whether the data can be reasonably modeled by a normal probability distribution, we need to decide how to estimate the probability of observing a certain concentration of cadmium in the Sarcannian forest groundwater. Your approach to estimating this probability depends on whether the data can be reasonably modeled by a normal probability distribution. As a quick refresher, let’s walk through and practice using two approaches to estimating this probability. Page 6

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