Traits and More Traits

Transcription

1 activity 26 Traits and More Traits BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 4 Quarter 3 Activity 26 SC.F The students knows that living things are different but share similar structures. SC.F The student knows that many characteristics of an organism are inherited from the parents of the organism, but that other characteristics are learned from an individual s interactions with the environment. SC.H The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H The student knows that to compare and contrast observations and results is an essential skill in science. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at this grade level. 1. Tell students that the more they look at their inherited traits, the more they should see how unique they are. Have students write a one page biography about themselves. The biography should include all the traits they identified in this activity. Remind students that these must be inherited traits, not learned behavior, or a practiced skill. (Evaluate responses based on creativity, but be sure students stay with inherited traits and do not describe a skill they can practice and improve upon.) 2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. broward county hands-on science Quarter 3 299

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3 activity 26 Traits and More Traits OBJECTIVES Students observe a variety of physical traits and determine the gene combinations needed to express those traits. The students observe six of their physical traits determine what combination of genes are needed to express each trait observe and compare the physical traits of their classmates recognize that each person is unique because no two people have exactly the same set of traits SCHEDULE About 30 minutes MATERIALS For each student 1 Activity Sheet 26, Parts A and B 1 mirror, hand* *provided by the teacher PREPARATION 1 2 Make a copy of Activity Sheet 26, Parts A and B, for each student. Collect and distribute hand mirrors if they are available. BACKGROUND INFORMATION In this activity, students look at traits that show complete dominance. That is, one gene is completely dominant to another and the recessive gene is not expressed. But, in general, inheritance in humans is much more complex. Relatively few traits are determined by only a single gene. Sometimes a dominant and a recessive gene together produce a blended trait instead of the dominant gene masking the recessive gene. For example, blending occurs when a gene for straight hair is paired with a gene for curly hair. The combination results in the individual having wavy hair. With still other traits, more than two genes are involved. For example, having brown eyes seems to be dominant to having blue eyes, but some people have hazel or green eyes, and there are many shades of brown. So many possibilities exist because eye color is determined by combinations of many genes. What happens when you begin to look at more than one trait in people? The many possible variations in an individual s thousands of traits offer so many possible combinations that no two people will have the same combination. Each person is unique. broward county hands-on science Quarter 3 301

4 Activity Sheet 26, Part A Activity Sheet 26, Part B Traits and More Traits Traits and More Traits Key D = dominant gene R = recessive gene Record a different student s name in each column. Begin with yourself. Write a D or an R for each trait according to your observations and the pictures shown on Activity Sheet 26, Part A. Trait Me Student 1 Student 2 Little finger bent or straight? Answers will vary. D Freckles R No freckles D Turned-up nose R Straight nose Hair or no hair on middle of finger? D No tongue folding R Tongue folding Nose turned up or straight? Freckles or no freckles? Tongue folds back or doesn t fold? Ear point or no ear point? Record the gene pair combinations that results in each of the traits you show by writing a D for a dominant gene and an R for a recessive gene. Possible combinations include DD, DR, and RR. If more than one gene combination is possible for a trait, record all possible combinations. D Straight little finger R Bent little finger Little finger bent or straight? Hair or no hair on middle of finger? Nose turned up or straight? Freckles or no freckles? Tongue folds back or doesn t fold? Ear point or no ear point? Answers will vary. D Hair on middle finger R No hair on middle finger D Ear point R No ear point 1 Guiding the Activity Distribute a copy of Activity Sheet 26, Part A, to each student. Have students look at the pictures of inherited traits on the activity sheet. (See Figure 26 1.) Describe each trait. If possible, find someone in the class who shows each trait so that all students can observe the traits firsthand. Additional Information Tell students that the D in the pictures stands for a dominant trait, and the R stands for a recessive trait. Ask, What gene pair must you have to show a trait that is marked D in the pictures? Remind students that they inherited one gene of each pair from their mother, and one from their father. Ask, What gene pair must you have to show a trait that is marked R in the pictures? 302 activity 26 Traits and More Traits To show a dominant trait, you must have at least one dominant gene in the pair that controls that trait. The other gene of the pair can be either dominant or recessive. To show a recessive trait, you must have two recessive genes in the pair that controls that trait.

5 D Freckles R No freckles D Turned-up nose R Straight nose D No tongue folding R Tongue folding D Straight little finger R Bent little finger D Hair on middle finger R No hair on middle finger Figure Some dominant and recessive traits. D Ear point R No ear point broward county hands-on science Quarter 3 303

6 2 3 4 Guiding the Activity Distribute a copy of Activity Sheet 26, Part B, to each student. Tell them that they are going to observe and record six of their own traits on the first chart. Then they will determine what genes they have that determine those traits. Have students decide which version of each trait they show and record either a D or an R for each trait in the Me column of the first chart. Remind them that an R represents a recessive trait and a D represents a dominant trait. Have students record the gene pair that is responsible for each of the traits they show in the second chart. If more than one gene combination is possible, they should record all possible combinations. Ask, What gene combination represents a recessive trait? Ask, What gene combination represents a dominant trait? Ask, Can you be sure what genes you have if you show a dominant trait? Explain. Now have each student choose two classmates and record their initials under Student 1 and Student 2 in the first chart. Have students observe the first trait, bent or straight little fingers, in their two classmates and record either a D or R for the trait. Additional Information Students should use Activity Sheet 26, Part A, for reference. Have hand mirrors available if students need them to observe their traits. Students should record both DD and DR if they show a dominant trait. They should record RR if they show a recessive trait. Two R genes represent a recessive trait. Either DD or DR genes can represent a dominant trait. No. You know only that you have at least one D gene. You may prefer to assign students into groups of three. 5 Ask, Are your two classmates like you in this trait? Have students observe the remaining five traits in their two classmates and record either a D or R for each trait. After they observe each trait, ask again if their two classmates are like them in this trait. When they have finished observing all six traits, ask, What is happening to the number of students with the same set of traits as you? 304 activity 26 Traits and More Traits Answers will vary. Students should notice that as more traits are observed, fewer students have all the traits in common.

7 6 Guiding the Activity Tell students that they have thousands of traits, although they have observed only six of them. Ask, If you could observe all your thousands of traits, do you think anyone in your class would match all the same traits as you? Additional Information Students should suggest that when all traits are considered, there are too many possible combinations for any two people to have the same traits and the same set of genes. R EINFORCEMENT Have students consider the traits of a relative, such as a sister or brother, and the traits of their best friend. Have them determine who has more matching traits to theirs. Have students suggest a reason why. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. broward county hands-on science Quarter

8 Connections Science Extension Suggest that students work in small groups to write rap songs about traits, using concepts and terms they have learned so far. Let each group find or create recorded musical accompaniment for its song and then perform it. If students have access to a video camera, they might prefer making a video rather than performing live. Science and Careers Invite a statistician to visit the class and ask him or her to explain in simple terms why it is not likely that any two people will have all their traits in common. Ask the visitor to introduce a discussion of probability by using the tossing of first one coin and then several coins. Science and the Arts Suggest that each student or group create a collage showing the many variations that occur in one particular feature, such as the nose or eyes. Students can cut pictures from magazines and newspapers or photocopy pictures in books. Create a classroom display of students collages. Science and Math Have students choose a trait such as eye color, and count the number of students in the class who have each eye color. Have students calculate the percentage of students in the class with each eye color. Guide them in this activity by telling them to divide the number of students with each eye color by the total number of students in the class and multiply the answer by 100. Then, ask each student to construct a pie chart showing the distribution of eye colors. Science, Technology, and Society Explain that a wide variety of skin colors are produced by only a few genes. Like skin color, color photographs in books and magazines are produced with only four colors of ink. Have students examine color photographs with a magnifier, identify the four colors (magenta, yellow, blue, and black), and observe how the number of dots of each color and their placement create the full-color image we see from a distance. 306 activity 26 Traits and More Traits