One Trait, Two Traits Dominant Trait, Recessive Trait Sarah B. Lopacinski Rockingham County

Transcription

1 Topic: genetics, Gregor Mendel Overview This lesson deals with genetic crosses, dominant and recessive genes, and Punnett squares. Before doing this lesson, students should have a background of Gregor Mendel and the experiments he did with pea plants. Students should know the following terms: genetics, traits, heredity, dominant, recessive, hybrid, and allele. Grades 7-12 Time Allotment One 90-minute block Learning Objectives On completion of this lesson students will be able to: explain and demonstrate the use of Punnett squares in predicting genetic crosses explain how to make predictions on whether offspring will show dominant or recessive traits explain the difference between genotypes and phenotypes. This lesson addresses Va. Science SOLs: LS.13. Media Components Student laptops with airport or computer lab. Laptops should have Internet Explorer or Safari and should have the following plug-ins: Shockwave , Quicktime TV with AV key or SmartBoard, Video clip Genes, Genetics, and DNA, Rainbow, United Learning. 15 March Segments: An Introduction to Genes, Genetics, and DNA (00:48) and Gregor Mendel s Rules of Heredity: Using Punnett Squares (05:04). Overhead projector Website: Materials and Student Handouts Notebooks and pencils-one per student Blue cards and brown cards cut out of construction paper -one card per student Handouts: Are You Dominant? and Practice with Punnett Squares -one each per student, attached Transparency of Are You Dominant? A plastic bag with 4 white socks and 4 black socks 1 penny per pair of students Transparencies of warm up questions, Mendel s pea crossings, Mrs. L s family, Punnett squares - attached Page 1 of 11

2 Teacher Preparations **Note to teachers: You may need to make certain that in your life science or biology text that there is a lesson prior to this teaching students of Gregor Mendel s experiment with inherited traits and genetics. Prior to the lesson students need to have an understanding of dominant, recessive traits, hybrids, alleles and the basics of genetics. Bookmark on your PortaPortal site: explorelearning.com. This site offers a limited free membership and you will need to be familiar with this site. Download videostreaming or burn to a CD prior to class Duplicate student handouts Make transparencies Create warm-up activity transparency (See Introductory Activity for questions.) Gather materials Make blue and brown cards Reserve laptops or lab, if necessary Introductory Activity 1. Focus: As students come into the classroom, hand each either a brown card or a blue card. Students should begin the warm up on the overhead projector. This will prep them for today s lesson. Activity: Questions for warm up: 1. What are alleles? 2. What controls alleles? 3. What is a dominant allele? 4. What is a recessive allele? 5. What occurs when you have one dominant allele and one recessive allele? Follow-up: Expected answers to be discussed after a few minutes 1. different forms of a gene which controls traits 2. genes 3. a trait that always shows up in an organism when it is present 4. a trait that is masked when a dominant trait is present but will show if two recessive alleles are present 5. a hybrid 2. Focus: When you came in, I gave each one of you a blue card or a brown card. Why do you think I gave you two different colored cards? (Expected answers: It represents eye color or There are two basic colors of eyes in humans. ) How many of you know the eye color of your family members? Activity: We re going to use my own family for an example. (Put up the transparency, Mrs. L s Family. ) There are seven girls in my family. My Dad had blue eyes, my mom has brown eyes, two sisters have brown eyes and five have green/blue eyes. How can this be? Shouldn t all of us have brown eyes if brown is the dominant color? Or wouldn t half be blue and half be brown-eyed? Follow-up: Why do you think this happens? (expected answers: some might guess that Mom had a hidden trait, others might not know until the lesson is done) This lesson is going to help us find reasons for this. 3. Focus: I ve put up a transparency of Mendel s Pea Crossings up on the overhead. We ll look at it to see if it can help us explain how genetics works. Activity: Read and discuss the transparency with the class. Page 2 of 11

3 Follow-up: In Mendel s first crossing, he crossed pure dominant tall with recessive short. In the F1 generation, he got all tall plants. What happened in the F2 generation is that the allele for short plants showed up 1/4 times. That is what happens with eye color too. Learning Activities 1. Focus: Are there more people in the world with brown eyes than blue? Are traits that are dominant more common in a population than traits that are recessive? Make a prediction. (Allow time for students to either write down their predictions and record them on a whiteboard.) We re going to watch a video segment and we will see some traits that some people have and others do not. Look for those traits as you watch. Play: Start videostreaming at beginning of Genes, Genetics and DNA. Pause: Time: 00:48 Audio cue: Let s find out more about genes, genetics, and DNA. Visual cue : girl wiggles ears. Follow-up: What were some of the traits? (some expected answers: double jointedness, dancing knuckles, tongue rolling) 2. Focus: We are going to see if more of us have dominant traits over recessive traits. You will need to sit with a partner. (Pass out and go over Are You Dominant? worksheet with the students and describe what each of the traits are: smile dimples, no smile dimples, earlobes attached/earlobes free, cleft chin/no cleft chin, hair on fingers/no hair on fingers, curly hair/straight hair.) When you and your partner finish, make a tally on the overhead transparency chart. Activity: Students make a chart of dominant and recessive traits and then place their tally marks on the transparency sheet the teacher has placed on the overhead. Follow-up: Look at our tally. What do you notice about these traits? (expected answer: Dominant traits don t always occur more often, sometimes, less often.) 3. Focus: (Have bag with socks.) I have a bag with 4 white socks and 4 black socks. What are my chances of reaching in right now and pulling out a white sock? (expected answer: 1/2 or 50:50 Demonstrate by pulling out a sock.) Was your prediction correct? (expected answers: maybe, maybe not) Probability is the predicted likelihood of an outcome. We can t say something is definitely going to happen. Activity: We will demonstrate probability with a coin toss. Each pair come and get a coin and keep track of how many times you get heads and how many times you get tails. Follow-up: (Tally up their results on the overhead.) Look at our results. Do you notice anything unusual? Just like a coin toss, our physical traits are not always accurately predicted. What we can do is make a prediction. 4.Focus: Let s see what Mendel said about predictions in this next segment of videostreaming. Take note of the chart that the video will show you of a black and white rabbit cross. Start videostreaming at Time: 0:00 Page 3 of 11

4 Audio cue: your height and even the shape of your nose. Visual cue: three kids looking in a mirror. Pause: Time: 5:04 (end of clip) Audio cue: 75% purple and 25% yellow, 3:1 Visual cue: teacher looking at corn ear with students. Follow-up: What did you notice about the chart of the rabbits? (expected answer: three of the rabbits were black and one was white. Go back and replay from 1:10-4:20, which shows how to do Punnett squares.) Stop at 4:20. Culminating Activities 1. Focus: Notice how the rabbit s fur color may have been black but they could potentially have an offspring which was white. We call the physical trait shown phenotype but what the genes say is genotype. So potentially, a rabbit might have a phenotype of black but its genotype may be Bb, which means it has one gene for black from one parent but a white gene from the other parent. The same is true for eye color. My mom had to have a gene for blue eyes; otherwise, all seven of her children would have been brown eyed. (Demonstrate this again with the transparency Mrs. L s family. Show the portion that has a Punnett square.) These squares can help us predict genetic crosses. A geneticist named Reginald Punnett created them. We are now going to use laptops (or computer lab) to learn how to do a Punnett square. Activity: Hand out laptops. Direct students using my computer/tv/av key (or smartboard) how to turn on computers: log in click on Safari go to portaportal.com, log in as a guest of slopacinski. under Science sites, choose Explore Learning. on Explore Learning, click on Science Gizmos under G6-8 Life Science, choose Heredity, genetics and diversity. Choose Mouse Genetics. Demonstrate how to choose mice to mate for eye color and fur color. Show students how the phenotypes are sometimes different from the genotypes. Some mice may have black fur but their genotype shows that they carry a gene for white. Allow students time to explore different crosses and also to do the Chicken Genetics which shows how traits can blend in some species. Follow-up: (Use protocol to close down computer, collect laptops.) What did you learn about Punnett squares? (expected answer: they can predict outcomes of genetic crosses and show phenotype and genotype of specific traits.) 2. Focus: You are now ready to do some Punnett squares to predict outcomes of genetic crosses. (Hand out Practice with Punnett Squares worksheets. Activity: Go through the example with them, using a transparency of the worksheet. Students will do the sheet independently. Circulate to make certain students understand. Follow-up: (Go through the sheet with the students, using the transparency to show how Page 4 of 11

5 to do the answers. Review the lesson by summarizing.) We learned today that the likelihood of an outcome is probability. Yet we can t say for certain that an outcome is definitely going to happen. Genes are random. We can only predict the outcome of an genetic cross using Punnett squares. The squares can predict whether the offspring will have a dominant trait, recessive trait or sometimes have the dominant trait but carry the gene for the recessive trait. What is this called? (expected answer: hybrid) Tonight, it would be interesting if you checked with your parents and siblings to see what traits they have. You could use your Are you Dominant? sheet to check. Assessment Practice with Punnett Squares worksheet Teacher observation during lesson Community Connections Using what they now know about phenotype and genotype, students will find out the phenotypes and genotypes for eye color of parents, grandparents and siblings. Cross-Curricular Extensions Math Survey peers with regard to dominant and recessive traits. Make graphs to display data. Research other dominant and recessive traits and do a survey among peers. Make different types of graphs to display data. Technology Take pictures with a digital camera of the different traits to make a bulletin board to display the graphs and photos. About the Author Sarah Lopacinski is a seventh grade science teacher at Montevideo Middle School in. This lesson was written as part of the Spring 2005 WVPT NTTI for the Virginia Enhancing Education Through Technology Ed Tech Grant awarded to the Shenandoah Valley Technology Consortium (SVTC). Mrs. L s Family Page 5 of 11

6 Dad had blue eyes Mom has brown eyes They had 7 daughters: #1 has brown eyes #2 and # 3 twins have blue eyes #4 has brown eyes #5 has green/blue eyes #6 has blue eyes #7 has green/blue eyes Page 6 of 11

7 When Gregor Mendel crossed his first set of pea plants he made sure that he only had only pure tall and pure short plants. T stands for tall because it is dominant and t stands for short because it is recessive. There are two letters because each plant got an allele from two parents...one from mom plant and one from dad plant. The P1 (parent) generation is written as TT tt x T T t t When he crossed these, Mendel was surprised that all the offspring were tall! These offspring are called the F1 generation. The shortnesstrait disappeared! What happened when he crossed the F1 generation was astounding! T t T TT t tt Page 7 of 11

8 Circle the trait that you have. The dominant trait has a * on it. Traits Free ear lobes* Attached ear lobes Hair on fingers* No hair on fingers Widow s peak* No widow s peak Curly hair* Straight hair Cleft chin* No cleft Smile dimples* No smile dimples Practice with punnett squares Page 8 of 11

9 Name Example: Cross red and yellow flowers where red is dominant over yellow. RR X rr red yellow phenotype 100% red 0% yellow genotypes 100% Rr (hybrid) 0% RR r(dominant) 0% rr (recessive) 1. Cross a red flower (Rr) with a yellow flower (rr) phenotype genotype % red % yellow % Rr %RR % rr 2. Cross two reds Rr X Rr phenotype genotype % red % yellow % Rr %RR % rr Page 9 of 11

10 3. Cross black and white rabbits where black is dominant over white bb X Bb phenotype genotype %black % white %Bb %BB %bb 4. BB x Bb phenotype genotype %black % white %Bb %BB %bb 5. bb x bb phenotype genotype %black % white %Bb %BB %bb Page 10 of 11

11 Quality Technology Questioning Use/Rec Good Good Good Yes Page 11 of 11