Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
62 i n ut e s e ss io RY - 1 50 -m ACTIVIT Y OVERVIEW LA O 40 to ns Analyzing Genetic Data BO RA T SUMMARY Students quantify the results of the seeds they germinated in Activity 55, “Plants Have Genes, Too!” They then compare their results to Mendel’s results. KEY CONCEPTS AND PROCESS SKILLS 1. Experimental results do not give ratios that perfectly match theoretical predictions. 2. A larger sample improves the reliability of experimental results. 3. Genetic results obtained from one organism can often be applied to others, providing an example of the unity of life. 4. The 3:1 ratio observed by Mendel for the offspring of a hybrid cross can be observed for traits in other organisms. KEY VOCABULARY allele mutation dominant recessive heterozygous traits homozygous MATERIALS AND ADVANCE PREPARATION For the teacher * 1 Transparency 62.1, “Class Results” 1 Transparency 55.1, “Parent and Grandparent Plants” 1 overhead projector For each group of four students 1 petri dish of germinated plants from Activity 55, “Plants Have Genes, Too!” *Not supplied in kit Teacher’s Guide D-105 Activity 62 • Analyzing Genetic Data Check to be certain that the seeds have germinated and are ready for counting. They are ready to count when they are large enough for you to clearly distinguish between green seedlings and paler seedlings, which should account for 1/4 of the seedlings. If the seeds are not ready, postpone this activity until after Activity 63, “Show Me the Genes!” However, be sure to complete this activity before starting Activity 64, “Nature and Nurture.” TEACHING SUMMARY Getting Started 1. Review students’ predictions from Activity 55, “Plants Have Genes, Too!” Doing the Activity 2. Students count and report their seed data. 3. Students analyze the class’s data. Follow-Up 4. The class discusses students’ results and reviews the genetic principles they illustrate. Extension Students post their results on the SALI page of the SEPUP website and compare their results with results from other classes. D-106 Science and Life Issues Analyzing Genetic Data • Activity 62 TEACHING SUGGESTIONS GETTING STARTED 1. they have just done to those of Mendel and to the critter-breeding scenario. In each case, first-generation plants with two different traits for a characteristic produced offspring showing only one of the Review students’ predictions from Activity two traits. These second-generation plants pro- 55, “Plants Have Genes, Too!” duced offspring in which approximately 1/4 of the Remind students that seeds are the result of sexual reproduction. Display Transparency 55.1, “Parent and Grandparent Plants,” to remind students of the crosses that produced the seeds they germinated. If you wish, you can begin by having the class discuss Procedure Step 1 of the activity, on page D-45 in the Student Book, or allow students to discuss it in their groups. Students’ experiences with the critters and Mendel’s results may lead them to change their predictions. Circulate around the room and listen to their discussions. offspring display the trait that had disappeared in their parents’ generation. Some students may notice the approximately 3:1 ratio of green seedlings:pale yellow seedlings, while others may need to be prompted to notice it. Encourage them to calculate the ratio from their results. Encourage thorough analysis of the results to prepare students for assessments on the “Analyzing Data” element of the D E S I G N I N G Students count and report their seed data. Students can usually distinguish easily between the green and pale yellow seedlings. Have each group of four prepare a summary of their results, which they should record in their science notebooks. They should report to you the number of green and pale yellow seedlings they observe. Use Transparency 62.1, “Class Results,” to display the class’s results. Students should record the class’s totals in their science notebooks as well. Fast finishers can go on to answer Analysis Question 1 while waiting for the class results to be posted. 3. Students analyze the class’s data. Discuss the results the class obtained. Ask them to C O N D U C T I N G I N V E S T I G AT I O N S (DCI) variable later in the course and for writing a lab report for Activity 64, “Nature and Nurture.” FOLLOW-UP DOING THE ACTIVIT Y 2. AND 4. The class discusses students’ results and reviews the genetic principles they illustrate. Use Analysis Question 1 to discuss the concept of dominant and recessive traits. The students’ predictions may have included the idea that the green would be dominant because green is darker than yellow. Remind them that the darker color isn’t always dominant. Refer to the seed-color trait in Activity 60, “Mendel, First Geneticist”; the yellow trait is dominant over green in this case. Point out that the plant characteristic the students are studying is similar to the ones that Mendel described, in that the characteristic has only two traits. There are no in-between, striped, or spotted colors. summarize the results and suggest their conclu- Display the results on Transparency 62.1 while the sions. Encourage them to compare the experiment class discusses Analysis Questions 2 and 3. Students Teacher’s Guide D-107 Activity 62 • Analyzing Genetic Data may need help understanding Analysis Question 4. SUGGESTED ANSWERS Use Transparency 55.1, “Parent and Grandparent TO ANALYSIS QUESTIONS Plants,” to help them think about this question. The 3:1 ratio of green:pale yellow seedlings strong- 1. Look back in your science notebook for the prediction you made in Activity 55. Was your predic- ly suggests that the parents of the seedlings have tion correct? Explain. one yellow and one green allele. Analysis Question 4 can be used to assess students’ understanding of Student answers will depend on both their pre- what the results suggest about the alleles of the par- dictions and their data. Look for the ability to ent generation. Score responses with the U N D E R - compare the actual data to their predictions. A S TA N D I N G possible example follows: C O N C E P T S (UC) scoring guide. Emphasize the idea that the students’ results from My prediction was wrong. I predicted that some one experiment suggest that the pale yellow color of the offspring would have striped green and trait of Nicotiana follows the Mendelian model for a yellow leaves, but they were either yellow or recessive trait, but do not provide absolute proof. green. I thought the green and yellow traits However, additional experiments have confirmed would mix, but they did not. that the pale yellow seedlings are the result of a single mutation and that the trait is recessive. 2. Compare the class’s results for seedling color to Mendel’s results for various pea plant After discussing the students’ results, explain to traits. Why are they similar? What do they suggest them that every sexually reproducing organism about the inheritance of the pale yellow and green studied, including humans, displays traits that fol- Nicotiana traits? low Mendel’s model of inheritance. In Activity 65, Many students will state that their results are “Breeding Critters—More Traits,” they will simulate similar to Mendel’s because their ratios of 3:1 some other, more complicated, patterns of inheri- green: pale yellow seedlings are similar to tance and how they relate to the basic Mendelian Mendel’s results for pea plant traits. The disap- model. They will learn more about human traits in pearance of the pale yellow trait in the second Activity 66, “Patterns in Pedigrees,” and some of the generation and its reappearance in the third following activities. generation is similar to Mendel’s result for dom- Extension inant and recessive traits. These results suggest that the pale yellow and green Nicotiana traits Students post their results on the SALI page of the are inherited in the same way as the pea traits SEPUP website and compare their results with Mendel studied. Results not fitting Mendel’s results from other classes. model (a ratio far from 3:1) may suggest that D-108 This provides a larger sample size. Instruc- the sample size was too small. You may wish to tions for posting your classes’ combine data from several classes, as suggested results are provided on the SALI in the Extension. Another possible source of page of the SEPUP website. error is attempting to distinguish between Science and Life Issues Analyzing Genetic Data • Activity 62 green and pale seedlings before they have This cross is similar to the one modeled in grown enough for the colors to be obvious. Activity 59 in that both of the parents in each 3. cross had a recessive trait that appeared in a Do each group’s results fit Mendel’s model? fraction of their offspring. You can infer the Explain. 4. presence of the recessive trait from the reappa- The groups’ results may fit Mendel’s model, but rance of the pale yellow trait in the third gener- many may not fit as well as the overall class’s ation, similar to the reapparance of the orange results. Many groups may get ratios that are not tail trait in the third generation in the critters. as close to 3:1. The larger the sample size, the The near 3:1 ratio that should be observed in greater the chance that the results will give a the whole class data for seedlings is statistically 3:1 ratio. and theoretically identical to the ratio obtained in Activity 59. When you first set out these seeds to germinate, you were told that they were all the offspring of two 5. Construct a Punnett square to show what will hap- green parent plants. You were also told that each of pen if one of the green parent-generation Nicotiana the green parents had one green parent and one yel- plants is crossed with a pale yellow plant. Explain low parent. the results. a. Based on the class’s results, what can you con- Assuming students use G for the dominant clude about the color alleles of each of UC the green parents of your seedlings? green trait and g for the recessive pale yellow A level 3 answer follows: trait, their squares should look like the one below. The Punnett square shows that half of the offspring will be green and half will be yel- The appearance of the yellow trait in approxi- low. If the green parents were homozygous, mately 1/4 of the seedlings provides evidence none of the offspring would be yellow. that each of the parent plants had a recessive g G allele for yellow color. This suggests that each parent had one green and one yellow allele for color. (A level 4 answer might include a Punnett square or might add that the parent plants were g Gg gg g Gg gg heterozygous, if you have stressed the terms heterozygous and homozygous.) b. How is this breeding cross similar to the one you modeled in Activity 59, “Gene Combo”? Explain. Teacher’s Guide D-109 Class Results Germinating Plants Results ©2006 The Regents of the University of California Student Group No. of Green Seedlings No. of Yellow Seedlings Totals Science and Life Issues Transparency 62.1 D-111