To learn about Gregor Mendel's discovery of a process of biological evolution: how recessive and dominant traits are passed from one generation of living organisms to the next.
In middle school, students start to learn about genetic traits (Benchmarks for Science Literacy, p. 108.), where they come from, and how they are passed down from parents to their offspring. But students do not start learning about evolution and how it exists through natural selection until high school. In high school, students will need to understand not only the concept of evolution, but also the evidence that supports it, such as historical experimentation and observation. Benchmarks also promotes learning about scientific advances through history, which this lesson aims to do.
The lesson, constructed around Gregor Mendel's 1865 paper, is one in history, scientific inquiry, methodology, classical genetics, and plant biology. Because of the extensive reading and discussion involved in this lesson, we consider it an advanced lesson. We have also built the lesson around the first half of Mendel's paper, because of the length of the paper, and because enough pertinent information is discussed in the first half. Of course, if you have the time and your class enjoys the format, we encourage you to cover the second half on your own, or to assign students homework based on the second half.
You will want to do this lesson with juniors and seniors who have had preparatory college biology classes. They probably have not yet read the Origin of Species; however, before this lesson, they should know about Darwin and have an understanding of the theory of evolution. This lesson only addresses how Mendel's work supports biological evolution—it does not get into the details of the rediscovery of his work, or the other supportive evidence of biological evolution.
You will guide students through a thorough discussion of the (first half of the) paper Mendel wrote about his pea plant experiments. This discussion/seminar type of format will give students an opportunity to partake in the class verbally and to learn to lead and direct discussion as well as ask pertinent questions regarding Mendel's paper.
You should be aware of several common misconceptions as you conduct this lesson. According to research: "High-school and college students, even after some years of biology instruction, have difficulties understanding the notion of natural selection. A major hindrance to understanding natural selection appears to be students' inability to integrate two distinct processes in evolution, the occurrence of new traits in a population and their effect on long-term survival. (Benchmarks for Science Literacy, p. 343.) This lesson may help students overcome the former—the occurrence of new traits in a population. You will discuss the latter—the effect on long-term survival.
Using the A Mendel Seminar esheet, have students explore Pea Experiment. This is an online interactive activity in which students will breed their own hybrid pea plants starting with two parent plants and ending up with four child plants. They continue to pick parents and breed them to see how traits are passed down to the next generation of plants.
Once students get to the site, they will read the first page and click on the box, Begin the Experiment. Tell students to jot down what they breed for parents and what the results are for the offspring. Give students about 10 minutes.
Then discuss the following:
- What did you notice about traits in offspring peas? (Here students may or may not have noticed trends. One obvious trend is that when two exact parent peas are bred, the offspring all look like the parents. They may also have noticed that when two different parent peas are bred, they create offspring with various traits. Any answer is acceptable for this question. The point is to get them to think in the way that Mendel thought.)
- Do you think that the breeding of peas could demonstrate natural selection and therefore biological evolution? (This question helps you ascertain students' current understanding of natural selection. Students should demonstrate that they understand the passing down of traits.)
- How might these traits affect the species as a whole? (Here is an opportunity to look for misconceptions as stated above. With the pea plants, it may not be as obvious. You may need to bring up traits of other organisms. For example, how would the trait of longer legs affect a generation of deer? Possible answers could include they may run faster and therefore survive better.)
You will probably have some class time left after the motivation. Using the A Mendel Seminar student esheet, tell students to go to Experiments in Plant Hybridization (1865), by Gregor Mendel and read the first section, Introductory Remarks, of the Mendel paper. (It should only take five minutes.) Then ask them the first question from the A Mendel Seminar: Teacher Sheet.
If you still have class time left, students can read the second section (ten minutes) and you can discuss the second discussion point from the same sheet.
Assign students to read the first half of the original text of Experiments in Plant Hybridization (1865), by Gregor Mendel and How to Prepare for a Seminar, for the next class in which a seminar will be held. These can be accessed from the student esheet. They will read from wherever you left off in class through section eight. You can either pass out copies of the paper, or send students online to read the full text.
Also, give students the MendelWeb: Flower Structure website, as a reference to use while reading. In Mendel's paper he uses flower "parts" to describe fertilization of the pea plants. Students can quickly glance at the diagram on this website to better understand what he is describing.
Class Two (and possibly Three)
A seminar discussion: Have students put their desks in a circle, and tell them that they will all discuss the assignment together. You may want to start the discussion, or ask a student to start the discussion. Tell students that they will be graded on participation. One thing you may want to keep in mind as the teacher is that you are a facilitator in this class, not a "leader." You should guide and keep a balance in the discussion. At the same time, if one of your students is on to something, you can ask them to elaborate, or ask if any other students have thoughts on the topic.
Start the discussion with ideas from the A Mendel Seminar: Teacher Sheet and use that sheet as you see fit.
Adaptation Recommendations: Though students should be ready at these grade levels to discuss things learned in class, you will have to decide if this format is appropriate for your class. One way to adapt the lesson for a group of students who are not ready to maintain a working discussion is to use A Mendel Seminar: Teacher Sheet literally. Ask the questions on the sheet and receive answers from students. You may be able to springboard from that approach to the seminar class format.
Assign students to read the rest of the paper for homework. You may opt to have a seminar discussion of the rest of the paper, or not. Either way, it will be beneficial for them to have read the entire paper for the summary and evaluation exercise.
Either distribute copies of A Mendel Seminar student sheet, or have students print the questions from the online esheet. Students will be assigned to a short take-home answer assessment on Mendel's experiment. You should see an improved understanding of the questions that were posed at the beginning of the class. In their answers, students should do the following:
- Students should show their awareness of Mendel's careful considerations and methodology throughout the experiment.
- In describing some of the results of Mendel's pea experiments, students should show an understanding of how recessive and dominant traits behave from generation to generation. This is an opportunity to recheck for the misconception: that there exists an occurrence of new traits in a population.
- They should describe how Mendel's breeding of peas demonstrated natural selection and in doing so also define natural selection and how it is part of biological evolution.
- When students discuss how he controlled his experiments, it is another opportunity to check for misconceptions. Students should link the new traits to possible long term survival, or not.
There are also some interesting papers and essays at MendelWeb. You can go to the list on the MendelWeb Table of Contents. We recommend: What Did Gregor Mendel Think He Discovered?, which discusses why Mendel's work was ignored for decades, and the issue of how Mendel should be "labeled." This article would address the "rediscovery" of Mendel's work.