“Chips” Off the Old Block?

By Susan Johnson

Notes to the Teacher:

Don Herbert (Mr. Wizard) has stated that he was successful at helping young people understand science concepts because he used the familiar (common household items) to explain the unfamiliar. By using analogies between common items or occurrences and science concepts we can be more successful at helping our students understand "the unfamiliar." Genetics is often described as a subject area in which many concepts are problematic for students. In order to "use the familiar to explain the unfamiliar" I decided to use cookies and their recipes as an analogy to organisms and their DNA "recipes." The first cookie lab I wrote using that analogy was entitled "Food for Thought: The Cookie Analogy." It allows classroom discussion of concepts such as genotype, phenotype, heredity, environment and natural selection. (It can be found in a publication of the National Association of Biology Teachers entitled "Favorite Labs From Outstanding Teachers; Volume II."1993) Another concept that causes difficulties for students is that of mutation. Many students assume that all mutations are harmful and can be easily detected on a phenotypic level. I designed this activity to exemplify the range of effects that mutations can have including the possibility that they might easily go undetected.

In the particular course in which I use this activity we begin with several introductory activities that raise issues that we attempt to resolve as the course proceeds. Later in the course we talk about DNA (transcription and translation) and the structure and function of proteins. At that point we revisit the activity to see how students might answer the some of the questions raised in that activity based on their new knowledge.

I hand out the recipes to the students several days before the activity so that they have adequate time to bake their cookies. They are all baking chocolate chip cookies, most will be using the traditional toll house recipe, but about one third of the students are given a recipe that contains a mutation. For example, their recipe might call for one egg instead of two, two teaspoons of vanilla instead of one, or no salt. They are to bring one dozen of their cookies to class on the day of the activity. I usually provide plates, napkins, cups and, of course, some milk!

Activity:

In this activity we are going to use the analogy of cookie recipes to that of the DNA "recipes" for living things to help us understand more about mutations. We are all going to bake the same type of cookie, the perennially favorite chocolate chip. Most of you will use the original recipe but a few will be given recipes in which an alternation (mutation) has occurred. The day of the activity of you will work in groups to make observations, including an "in depth enzymatic analysis," to determine whether a particular cookie was produced from a recipe that contained a mutation, and, if so, what might that mutation be.

Procedure:

Each class member will bake chocolate chip cookies using the recipe provided. Most of you will receive the copies of the traditional recipe seen below but some will be given copies of recipes in which a "mutation" has occurred.

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
1 teaspoon vanilla
2 eggs
1 package (12 oz.) chocolate chips

Preheat oven to 375°F. Beat together margarine, sugar, and brown sugar until creamy. Beat in eggs. Add vanilla. Combine flour, baking soda and salt. Gradually add to margarine mixture. Stir in chocolate chips. Drop by rounded teaspoonfuls onto ungreased cookie sheets. Bake for 8-11 minutes, until golden brown.

On the day of the activity bring one dozen of the cookies you baked and put them on a plate provided by the teacher (put your name on the underside of the plate). We will number the plates so that they can be identified for the class discussion. After your cookies are arranged on the plate get together with the members of your group and move from one plate to the next sampling pieces of the cookies on each plate. (If you try to eat a whole cookie from each plate your "in depth enzymatic analysis" could prove to be too "filling.")

Although you are analyzing the cookies as a group make sure you each keep a record as to whether or not you believe a particular cookie was produced from a recipe that contained a mutation. If you judge a particular cookie to be the result of a recipe that contained a mutation also include your tentative ideas as to what that particular mutation might be.

When all the class has had an opportunity to test each plate of cookies, we will take a vote as to the number of students who believe each to be the result of a recipe that contained a mutation. Students will also need to share their ideas as to what the mutation might have been. After we have taken each vote and shared ideas the student who baked that cookie will let us know whether or not it was produced from a recipe that contained a mutation. If yes, the baker of that cookie will also describe the particular mutation.

Questions for discussion:

1a. Was there always class consensus as to whether a particular cookie was produced from a recipe with a mutation?

b. If your answer to part a was "no", give an example and an idea as to why lack of consensus might have occurred.

2a. Were any cookies incorrectly labeled as being produced from a recipe with a mutation?

b. If your answer to part a was "yes" give an example and an idea as to why that particular cookie might have been mislabeled.

3a. Propose at least one tentative idea as to why some cookie mutations are more easily detected than others.

b. Since we are using cookies and their recipes as analogies for living organisms and their DNA "recipes", extend or modify the idea you proposed for 3a to explain why some mutations in humans are more easily detected than others.

Assessment/Evaluation

In the course for which this activity was written the students keep research notebooks as would practicing scientists. For this activity their notebook entry should include the number of each recipe, whether they thought each particular cookie was baked from a recipe in which there was a mutation, and, if so, what they think the particular mutation might be. They are also to record their answers to the questions that are included in the lab and a summary of our class discussion. That discussion of each cookie includes a vote on whether or not it was baked from a recipe that contained a mutation, what some class ideas were as to what the mutation might be and then the information from the student who used that recipe. The knowledge they gain from the activity is also assessed from the class discussion and notebook entries that follow the later portion of the course in which DNA and proteins are studied.

Extension/Reinforcement/Additional Ideas

Cookies, which I have even given their own species name "Crustula suavia" (Latin for "cookie sweet"), and their recipes are a great analogy that can be useful to teach many topics in biology, especially those in the subject areas of genetics and evolution. For example, discussion of why certain cookie recipes survive and why some are changed or become "extinct" is a good analogy for change over time. Why certain type of cookies are common to certain ethnic groups or geographic locations has proven helpful in discussing diversity. Questions used in the activity can easily be modified to promote discussion of a particular topic or topics and the students are quite involved in the activity because they make the cookies. For some students it is their first experience with baking, so I tell them that all cookies get an A.

Cookies can also be tied in nicely with a discussion of proteins and how some alterations in the DNA sequence may have no effect on the amino acid sequence or how some changes in the amino acids sequence may not affect the activity of that protein and thus not affect the resulting phenotype. Other mutations might affect the level of expression of a gene which may or may not have an effect on the phenotype. Each of these ideas can be reinforced with the cookie analogy as some changes in the recipe can result in changes in the type of ingredient or the amount of that ingredient and in either case might still go undetected.

Another variation to the activity can be used to discuss genetic engineering. In that case I let several students make changes in the recipe that they believe will improve the cookies and use that to discuss the genetic engineering of organisms.

Below are examples of the"mutated" recipes that I pass out to the students. You can use these or come up with some mutations of your own! If you have an suggestions for changes in either the orginal cookie lab in the NABT publication or in this activity, I would appreciate hearing about them.

Recipe A:

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
1 teaspoon vanilla
2 eggs
1 package (12 oz.) chocolate chips

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
2 eggs
1 package (12 oz.) chocolate chips

1 1/2 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
1 teaspoon vanilla
2 eggs
1 package (12 oz.) chocolate chips

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
1 teaspoon vanilla
1 egg
1 package (12 oz.) chocolate chips

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
3/4 cup sugar
3/4 cup firmly packed brown sugar
1 teaspoon vanilla
2 eggs
1 package (12 oz.) raspberry chocolate chips (or use any
type other than standard chocolate chips)

2 1/4 cups all purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 cup butter or margarine
1 1/2 cups sugar
1 teaspoon vanilla
2 eggs
1 package (12 oz.) chocolate chips

Fellows Collection Index

Activities Exchange Index