Inherited Traits BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN

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1 activity 25 Inherited Traits BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 4 Quarter 3 Activity 25 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. SC.H The student knows that a model of something is different from the real thing, but can be used to learn something about the real thing. SC. H The student knows that natural events are often predictable and logical. 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. Remind students that they made a model of a chromosome in this activity. Ask, Why did you use a model and not the real thing? (Answers will vary; models are used when the real objects are too small, too big, too hard to obtain, or events take too long to occur; they are also used to help us visualize something we cannot see.) Do we also need models to understand how a human cell works? (Yes, the cell and its parts are too small to see.) broward county hands-on science Quarter 3 289

2 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. 290 activity 25 Inherited Traits

3 activity 25 Inherited Traits OBJECTIVES In this activity, students learn about dominant and recessive genes and how they express themselves in physical traits. The students learn the difference between dominant and recessive genes use a model to explore how genes are passed from parent to offspring infer the traits of offspring based on the makeup of their gene pairs SCHEDULE About 40 minutes VOCABULARY chromosome dominant gene recessive gene MATERIALS For each student 1 Activity Sheet 25, Part A 1 box crayons* For each group of four 1 Activity Sheet 25, Part B 1 bead, square (same color as round beads) 3 beads, round, same color 2 pipe cleaners, short, dark-colored 2 pipe cleaners, short, light-colored *provided by the teacher PREPARATION Make a copy of Activity Sheet 25, Part A, for each student. Make a copy of Activity Sheet 25, Part B, for each group. Cut four light-colored and four darkcolored pipe cleaners into four equal pieces each to make 16 short light and 16 short dark pipe cleaners. Divide the bag of beads up so that each group of students gets three round and one square bead of the same color. (It doesn t matter if two teams use the same color.) BACKGROUND INFORMATION Chromosomes are tiny structures found in the nucleus of a cell. Each human cell contains a set of 46 chromosomes, one pair each of 23 different chromosomes. Each chromosome carries many genes, which code for traits. Genes for all of an individual s traits are found on these 23 pairs of chromosomes. An individual gets one chromosome of every pair from each parent. Many traits are determined by a single pair of genes. When both genes for the trait are the same, such as for brown eyes, the individual has brown eyes. When both genes are for blue eyes, the individual has blue eyes. But what happens if an individual has one gene for brown eyes and one gene for blue eyes? The gene for brown eyes masks the gene for blue eyes, and the individual has brown eyes. The blue-eyed trait is not expressed. The gene that masks the other and is expressed is called a dominant gene. The gene that is masked and not expressed is a recessive gene. Thus, brown eye color is a dominant trait, and blue eye color is a recessive trait. Brown-eyed individuals can have either two identical genes for brown eye color or one gene for brown and one gene for blue. These two individuals are indistinguishable externally. Only one combination of genes (blue/blue) will cause someone to have blue eyes. broward county hands-on science Quarter 3 291

4 Activity Sheet 25, Part A Activity Sheet 25, Part B Inherited Traits Inherited Traits 1. Use crayons to draw the pipe-cleaner-and-bead chromosome models for the mother and the father in the boxes below. 2. Then draw the chromosome models for each child they made. Key Dominant gene: Recessive gene: Mother Father Mother s Chromosomes Father s Chromosomes Child 1 Child 2 Child s Chromosomes Can Child 1 roll his or her tongue? Explain? Answers will depend on whether or not the child has the dominant gene from the father. If the child has the gene, he will be able to roll his tongue. Can Child 2 roll his or her tongue? Explain? Answers will depend on whether or not the child has the dominant gene from the father. If the child has the gene, she will be able to roll her tongue. 1 Guiding the Activity Have students try to curl the two sides of their tongue toward the roof of their mouth. This trait is called tongue rolling. (See Figure 25 1.) Tell students not to be upset if they cannot roll their tongue. Some people can do it, and some people cannot. Additional Information If students cannot tell if they are rolling their tongue, have them ask a classmate. Figure Tongue rolling and non-tongue rolling traits. 292 activity 25 Inherited Traits

5 2 Guiding the Activity Remind students that genes are tiny structures in cells that determine traits. Children inherit genes from their parents. Write the term chromosome on the board. Tell students that genes are carried on structures called chromosomes. Chromosomes come in pairs. So genes also come in pairs. One gene for a trait is found on one chromosome of a pair, and the other gene for the same trait is found on the other chromosome of the pair. You inherit one chromosome of each pair from each parent. Tell students that tongue rolling, like many other traits, is controlled by genes. Children who inherit a gene for tongue rolling from both parents are able to roll their tongues. Children who inherit a gene for not being able to roll their tongues from each parent will not be able to roll their tongues, no matter how hard they try. Additional Information You may choose to draw a pair of chromosomes on the board and mark the location of a gene pair on each. (See Figure 25-2.) Gene A Gene A Figure A pair of genes on a pair of chromosomes. 3 Ask, What do you think happens when a child inherits a gene for being able to roll her tongue from her mother and a gene for not being able to roll her tongue from her father? Answers will vary. Encourage discussion. Write the terms dominant gene and recessive gene on the board. Explain that some genes are dominant, or powerful. Other genes are recessive, or weak. When a dominant gene is in a pair with a recessive gene, the dominant gene is the one that comes through. In the case of tongue rolling, the gene for being able to roll the tongue dominates, or overpowers, the gene for not being able to roll the tongue. So, a person with one gene for tongue rolling and one gene for nontongue rolling will be able to roll his or her tongue. Recessive traits are only seen when both genes in the pair are recessive. In the case of tongue rolling, only a person with two recessive genes for tongue-rolling will not be able to roll his tongue. broward county hands-on science Quarter 3 293

6 Guiding the Activity 4 Tell students that they will now create chromosome models that they can use to look at how different pairs of genes can be passed from parents to offspring. Additional Information Hold up a pipe cleaner with a bead on it. Explain that, in this model, the pipe cleaner will represent a chromosome and the bead will represent a gene on that chromosome. Dark pipe cleaners will represent chromosomes from the father. Light pipe cleaners will represent chromosomes from the mother. Square beads will represent dominant genes. Round beads will represent recessive genes. Write this key on the board so that students can refer to it as needed. 5 Distribute Activity Sheet 25, Part A, and a box of crayons to each student. Distribute pipe cleaners, beads, and Activity Sheet 25, Part B, to each group of four. Have students use the pipe cleaners and beads to make a pair of chromosomes for a mother with two recessive tongue-rolling genes as follows: place a round bead on one light-colored pipe cleaner and another round bead on another light-colored pipe cleaner. Fold over the ends of the pipe cleaners once the beads are on. Safety Note: Tell students to handle the pipe cleaners carefully. The ends may be sharp. Have students place this chromosome pair in the Mother s Chromosomes box on Activity Sheet 25, Part B. Now have students make a chromosome pair for a father with one dominant tongue-rolling gene and one recessive tongue-rolling gene by putting one round bead on a dark-colored pipe cleaner and one square bead on another dark-colored pipe cleaner. Have students place these chromosomes in the Father s Chromosomes box on Activity Sheet 25, Part B. 294 activity 25 Inherited Traits

7 6 7 Guiding the Activity Invite one student in each group to close his or her eyes and randomly choose one chromosome from the mother and one from the father and place them in the Child s Chromosomes box on Activity Sheet 25, Part B. Ask, What does this new chromosome pair represent? Ask, Are any dominant genes present in the child s chromosomes? Ask, Can this child roll his or her tongue? How can you tell? Have students record the results of this exercise on Activity Sheet 25, Part A. Tell students to put the child s chromosomes back into the boxes for the mother and father. Now, have them imagine that these parents have another child. Invite a second volunteer to close his or her eyes and randomly choose another chromosome from each parent and place the two chromosomes in the Child s Chromosome box. Additional Information It represents one pair of chromosomes in a cell of the child. Remind students that chromosomes exist in pairs within the cells in their body. One chromosome comes from the mother and one from the father. Answers will vary depending on which of the father s chromosomes was chosen. The child can roll his or her tongue if students have chosen the chromosome from the father that has a square (dominant) bead. If students have chosen the chromosome with a round (recessive) bead, the child will not be able to roll his or her tongue. Ask, Will this child be a tongue roller? How can you tell? Have students record the results of this exercise on Activity Sheet 25, Part A. The child can roll his or her tongue if students have chosen the chromosome from the father that has a square (dominant) bead. If students have chosen the chromosome with a round (recessive) bead, the child will not be able to roll his or her tongue. broward county hands-on science Quarter

8 R EINFORCEMENT Have students repeat Steps 5 7, making chromosomes for two tongue-rolling parents with one dominant gene and one recessive gene. If students choose the chromosome with the recessive gene from each parent, they will discover why children often have traits that neither parent has. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. C LEANUP Have students take apart their model chromosomes and place the beads and pipe cleaners back in the kit. 296 activity 25 Inherited Traits

9 Connections Science Extension Students might enjoy finding out how many chromosomes are in the body cells of other species besides humans. Encourage them to research a wide variety of organisms protists, plants, invertebrates, fish, amphibians, reptiles, birds, and other mammals, including our closest evolutionary relative, the chimpanzee. Science Challenge Have students make a list of some human traits that are inherited, then do library or Internet research to determine on what chromosome the gene that controls each trait is located. As students do research, they will discover that not all traits are controlled by a single gene. For example, skin color and height are determined by many genes. Also, some traits are determined by genes that blend together to form a new trait. For example, a person who has a gene for straight hair and a gene for curly hair will have wavy hair. Tell students to concentrate on finding out the locations of genes of simple traits that they have studied. Science and Language Arts Ask students to research the derivation and origin of the word chromosome. (from the Greek chromo, color, and some, body ) To be visible with a microscope, chromosomes must be stained with a colorful dye, thus giving rise to the term colored body. Science and Math Tell students that an adult human body contains about ten trillion cells. Ask students to write this number. (10 followed by 12 zeros). Now, tell students that human cells have 46 chromosomes. Ask them to calculate the total number of chromosomes in an adult human body. (10,000,000,000,000 cells 46 chromosomes = 460,000,000,000,000 chromosomes) Science and the Arts Many life science and biology textbooks published in recent years contain dramatic photographs of chromosomes, especially those that have been dyed with fluorescent dyes. In addition, some professional artists have created art based on structures such as chromosomes. Have students look through books to find such photographs and illustrations. broward county hands-on science Quarter

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