Science Life science heredity

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1 Topic Heredity Key Question What kind of offspring will our Teddy Bear parents produce? Learning Goals Students will: recognize that characteristics passed from parents to child are predictable, and simulate the mixing of genetic codes to determine the possible outcomes from two parents. Guiding Documents Project 2061 Benchmarks Some likenesses between children and parents, such as eye color in human beings, or fruit or flower color in plants, are inherited. Other likenesses, such as people s table manners or carpentry skills, are learned. For offspring to resemble their parents, there must be a reliable way to transfer information from one generation to the next. NRC Standards Many characteristics of an organisms are inherited from the parents of the organisms, but other characteristics result from an individual s interactions with the environment. Inherited characteristics include the color of flowers and the number of limbs of an animal. Other features, such as the ability to ride a bicycle, are learned through interactions with the environment and cannot be passed on to the next generation. Every organism requires a set of instructions for specifying its traits. Heredity is the passage of these instructions from one generation to another. Heredity information is contained in genes, located in the chromosomes of each cell. Each gene carries a single unit of information. An inherited trait of an individual can be determined by one or by many genes, and a single gene can influence more than one trait. A human cell contains many thousands of different genes. NCTM Standards 2000* Predict the probability of outcomes of simple experiments and test the predictions Design investigations to address a question and consider how data-collection methods affect the nature of the data set Collect data using observations, surveys, and experiments Represent data using tables and graphs such as line plots, bar graphs, and line graphs Use proportionality and a basic understanding of probability to make and test conjectures about the results of experiments and simulations Math Data analysis probability statistics sampling graphing bar graphs Science Life science heredity Integrated Processes Observing Classifying Collecting and organizing data Comparing and contrasting Generalizing Inferring Materials Teddy Bear Counters (see Management 3) Paper bag or box, one per student group Student pages Background Information Traits are passed between generations by genetic coding of chromosomes. One or more gene pairs may control a trait. Each parent contributing one gene forms a pair of genes. With a simple genetic characteristic, one gene pair controls the trait. If a gene s trait is more prominent in the individual, that gene is said to code for the dominant trait. If the gene s trait is less prominent in the individual, the gene is said to code for the recessive trait AIMS Education Foundation

2 The ability to curl your tongue is a trait that is controlled by one gene pair. A dominant gene will allow you to curl your tongue. A recessive gene will not give you this ability. If either or both of the genes in your pair is dominant you will be able to curl your tongue. If both the genes in your pair are recessive, you will not be able to curl your tongue. When both genes are the same, they are called homogeneous. If both parents are homogeneous for the recessive trait, all offspring will display the recessive trait because they have only recessive genes. If both parents are homogeneous for the dominant trait, all the offspring will display the dominant trait because they have only the dominant genes. When the gene pair is mixed with a dominant and recessive gene, it is called heterogeneous. Individuals that have heterogeneous genes display only the dominant trait. Many people who curl the their tongues (dominant trait) have heterogeneous genes (one dominant, one recessive). The offspring of heterogeneous parents show either recessive or dominant traits depending on which gene was passed on to the child. The mixture of traits in the offspring then is the result of the chance event of the recessive or dominant trait being passed on to the child. This mixture can be predicted using probability. This investigation is a simulation of experiments done by Gregor Mendel in the early 1800s. Mendel s work formed the foundation of the study of heredity. Mendel studied pea plants and recognized that dwarf plants always produced dwarf plants, while tall plants produce both dwarf and tall offspring. With pea plants, tall is a dominant trait. Dwarf plants have pure recessive genes. This investigation simulates the offspring of two heterogeneous parents. The two equal amounts of colored Teddy Bear Counters (20) represent the equal representation of dominant and recessive genes in the parents. Drawing two bears simulates the contribution of one gene from each parent. If red and blue are the colors, there are four possible outcomes in the draw. Only possibility is for both bears to be the same color red-red or blue-blue. These represent two homogeneous offspring. The other possibilities are redblue or blue-red, which represent two heterogeneous offspring. These possibilities mean that in a large sample, one-fourth should both be red, one-half should be mixed, and one-fourth should be both blue. When working with probability, it is important to gather information from a large number of events. Mendel often studied as many as 17,000 plants before arriving at a generalization. The requirement of using a large number of trials should be discussed and stressed as students complete this investigation. During the simulation each student group will repeat the investigation four times. The average will then be computed. Next, the average results from all groups will be pooled. This will yield a significant number of trials and the average result should closely approximate those Mendel found with pea plants. Just as Mendel found that about one-fourth of the results were pure tall, one-half hybrid, and one-fourth pure dwarf, students will find that one-fourth of the results consist of pairs where both are of the first color, one-half are mixed, and the remaining one-fourth are pairs of the second color. (Hint: use the terminology of first and second colors rather than color names, this helps avoid confusion since different groups will probably use different colors.) Students will learn how heredity is passed from parent to offspring through genes and will be able to generalize the pattern of distribution. However, they will have more difficulty understanding the probability controlling the outcome. Piaget conducted a similar investigation using marbles. He wanted to determine at what age students formed intuitive notions of probability. He placed an equal number of marbles of each of two colors in a bag and mixed them thoroughly. He told children that he would draw the marbles out in pairs. He asked them to predict which event was most likely among the following: both would be the first color; both would be the second color; or, there would be one of each color. He found that generally students before age 12 would make guesses, usually wrong, with little reason for doing so. However, at age 12 many of them began to reason that the most likely event would be a mixed pair. Recognize what understanding is most appropriate for your students. Before beginning this investigation, ask your students to make predictions as to the most common result and have them explain the reason for the answer. Key Vocabulary: Trait: a characteristic that is inherited from parents DNA: the material that carries our traits Gene: a part of the DNA that has our traits on it Management 1. The best results will be obtained if there are six to eight student groups each performing independent investigations. 2. Learning groups of three to four students work best. Each student should be assigned a job: drawer, grapher, recorder, calculator. The assignments can rotate after each test. 3. Each group will need 40 Teddy Bear Counters, 20 each of two colors. The AIMS Friendly Bears or other objects of uniform size and shape may be substituted for Teddy Bear Counters. Have students put the bears into a paper bag or box. Procedure 1. Discuss the Key Questions and relate the simulation to a parents genes being selected and paired and passed on to the offspring AIMS Education Foundation

3 2. Explain the procedure and divide the class into the desired number of collaborative learning groups and assign tasks. 3. Make sure that each group has a bag or box of 20 Teddy Bear Counters in each of two colors. 4. Explain to the students that the bears will be drawn out in pairs and not put back into the bag or box until the trial ends; 20 pairs will be drawn. Before beginning the investigation, ask the students to record their predictions of how many of the 20 events will occur for each of the three results. 5. Instruct the students to mix the bears thoroughly, pointing out that such mixing is necessary to produce random results. 6. Have students draw out bears in pairs, classifying each pair as it is placed on the sorting bar graph (page 2). 7. After all pairs have been classified, have students place the numerical information in the table. 8. Tell students to complete four trials before they find the average and graph the results. 9. Have all the groups share their results. Collect the data from all of the groups. 10. Have students find the average result of all the trials and graph the information. Connecting Learning 1. How do your results compare for the four trials? [different for each trial, but most in mixed pairs] 2. Why is the average a better predictor of what is likely to happen? [It balances the highs and lows.] 3. Which event (colors of bears) occurred most frequently? [mixed pairs] 4. How did the class average compare to your group s average? 5. How many times more often does a mixed pair occur than a pair of one of the colors? [twice as often as either of the colors] 6. If the 20 pairs represent 20 offspring, what fraction of the offspring will share the dominant trait with the parents? (Colored counters represent the dominant and recessive genes. Let the first color represent the dominant gene. If a pair of genes has one dominant gene, the offspring will show that trait.) 7. What fraction of the 20 offspring will not share the trait with their parent? 8. Why do offspring tend to have the same traits as their parents? 9. What are you wondering now? * Reprinted with permission from Principles and Standards for School Mathematics, 2000 by the National Council of Teachers of Mathematics. All rights reserved AIMS Education Foundation

4 Key Question What kind of offspring will our Teddy Bear parents produce? Learning Goals Students will: recognize that characteristics passed from parents to child are predictable, and simulate the mixing of genetic codes to determine the possible outcomes from two parents. Key Vocabulary Trait: a characteristic that is inherited from parents DNA: the material that carries our traits Gene: a part of the DNA that has our traits on it AIMS Education Foundation

5 1. Put 20 counters of a first color and 20 of a second color into a bag or box. 2. Mix them well. 3. You will pull the counters out in pairs. Before you start, predict how many of the 20 pairs there will be of each combination. Number of pairs where both are the first color: Number of pairs where there is one of each color: Number of pairs where both are the second color: 4. Draw out two counters at a time, classify the pair, and place both counters in the proper column on the bar graph on the next page. 5. After all the counters have been drawn, count the number of pairs in each category and record in the table. 6. Complete four trials and then average them. Test Number ONE TWO THREE FOUR TOTAL AVERAGE AIMS Education Foundation

6 Mixed Colors AIMS Education Foundation

7 Graph the results for each of the four tests. Test Number AVERAGE Result Number of Occurrences How do the number of occurrences for the type of events compare between trials? 2. Why is the average a better predictor of what is likely to happen? 3. Which event occurred most frequently? 4. How much more often did the most common event happen than either of the other two events? AIMS Education Foundation

8 Collect the average results from the other groups. Calculate the average for the class. Group Number ONE TWO THREE FOUR FIVE SIX SEVEN EIGHT TOTAL AVERAGE Graph the class averages. Number of Occurrences DESCRIPTION How did the class average compare to your group s average? 6. How many times more often does a mixed pair occur than a pair of one of the colors? AIMS Education Foundation

9 Connecting Learning CONNECTING CONNECTING LEARNING LEARNING 1. How do your results compare for the four trials? 2. Why is the average a better predictor of what is likely to happen? 3. Which event (colors of bears) occurred most frequently? 4. How did the class average compare to your group s average? 5. How many times more often does a mixed pair occur than a pair of one of the colors? AIMS Education Foundation

10 Connecting Learning CONNECTING CONNECTING LEARNING LEARNING 6. If the 20 pairs represent 20 offspring, what fraction of the offspring will share the dominant trait with the parents? 7. What fraction of the 20 offspring will not share the trait with their parent? 8. Why do offspring tend to have the same traits as their parents? 9. What are you wondering now? AIMS Education Foundation

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