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A Problem-Solving Simulation for Classical Genetics

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A Problem-Solving Simulation for Classical Genetics I 4. Problem-SolvingSimulation for Classical Genetics Jim Stewart For several years I have used Bio- 1. How many traits exist in the population? QUEST's Genetics Construction Kit or Downloaded from http://online.ucpress.edu/abt/article-pdf/58/8/478/47735/4450215.pdf by guest on 27 September 2021 GCK (1994) with high school and uni- 2. What are the trait names? versity students as well as their in- 3. How many genes code for each trait? structors. Instructors like GCK as it 4. How many variations exist for each trait? allows students to solve problems that 5. What are the names of the variations? require them to generate and analyze 6. How many alleles exist in the population for each gene? data as they reason from effects (given 7. How many alleles exist in an individual for each gene? phenotypes) to causes (underlying ge- 8. What combinations of alleles can exist in individuals within the population? netic mechanisms) that are, in part, 9. Will the genes that code for a trait assort independently of those for other responsible for the effects. Yet, there traits? (It is possible to have students develop models for meiosis with are always instructors who do not have linkage in which they have to consider the effects of different map enough computers to allow their stu- distances). dents to have the best experience with 10. If there is linkage, are the genes linked on autosomes or on the X GCK. So, for the last two years I have chromosome? been developing and using a non-com- 11. What are the "relationships" between the alleles? (Does one get expressed in puter version of GCK. the presence of the other-a relationship of dominance; or are they both expressed-a codominance relationship?). 12. How do the allele combinations identified in #8 map to the variations The Simulation identified in #5. (This forces students to think about heterozygosity and homozygosity). The simulation was designed to be 13. What are all of the cross possibilities, given the various allele combinations, used by groups of three or four stu- that can occur? dents each. Two groups are necessary 14. What are the phenotype outcomes of all of the crosses identified in #13? to conduct the simulation. During the simulation each group will assume two Figure 1. Questions used to design a problem structure. different roles. One is to generate prob- lems and the second is to be a research group, probing the problem created by for generating data for the research research group. To do this they need to the other group. The problem genera- group. consider the number of organisms to tor group produces a field collection of A good way for students to begin to be in it, how to make it look like a organisms and offspring for the crosses develop a problem structure is to an- random collection in terms of pheno- performed by the research group. The swer questions like those in Figure 1. type, sex, and in terms of its genotype research group performs crosses and Example answers to the questions for a distribution. They also need to decide interprets data in order to understand codominance problem are shown in if all possible phenotypes and geno- the genetics of the population they are Figure 2.1 While students need a basic types will be represented in the field investigating. The responsibilities of understanding of genetics in order to collection. The field collection is given the groups are as follows. develop a problem structure, their un- to the research group as a Field-Collec- The Problem Generator Group has derstanding of genetics will improve as tion Card (see Figure 3). two responsibilities. The first is to de- they develop the structures. The generator group also creates velop a structure for the genetics of the Once a group has developed a prob- Offspring Cards to provide to the re- problem (e.g. simple dominance, lem structure they use it to produce a search group in response to crosses codominance, multiple alleles, autoso- field collection of organisms for the that they perform. The number of cross mal linkage, etc.). Their second respon- possibilities will depend on the genetic the The students sibility is to use the structure as a basis I structure of problem. Note that genotypes (alleles) are repre- have to consider all possible genotype sented by numbers, rather than letters. I have done this because numbersare a more combinations that can be crossed and Jim Stewart is a Professor at the Uni- generic representationthan letters, particu- all of the possible offspring phenotypes versity of Wisconsin-Madison, 225 N. larly in solving problemswhere it is impos- that can be produced from those Mills St., Madison, WI 53705. sible to assign letter symbols prior to know- crosses. They then create Offspring ing how genes are expressed as variations. Cards to give to the research groups as 478 THEAMERICAN BIOLOGY TEACHER, VOLUME 58, NO. 8, NOVEMBER/DECEMBER1996 cross results to be given to the research 1. Number of traits? 1 group with little delay. 2. Name of trait? Antennae Shape Preparingthe structurefor the prob- 3. Number of genes (loci)? 1 lem, along with the Field Collection 4. Number of variations? 3 and OffspringCards, takes time. How- 5. Names of variations? Hooked; Knobby;Split ever, the knowledge of genetics gained 6. Number of alleles in the population? 2 is worth the effort.The structuresand 7. Number of alleles in an individual? 2 cards, once produced, can be used 8. Possible allele combinations? 1,1; 1,2; 2,2 again. 9. Independent assortment? Yes The Research Group has the respon- 10. X-linkage? No sibilities of using the field collection 11. Allele relationship? Codominant and the results from crosses to develop 12. Alleles to variation mapping? 1,1 Hooked; 1,2 Knobby;2,2 Split an explanation of the genetics operat- ing in the population. To produce off- 13/14. Cross possibilities? spring data they need to identify, for Male x Female Offspring3 the GeneratorGroup, organisms that 1. 1,1 x 1,1 All Hooked will be the parents of the next genera- 2. 1,1 x 1,2 1/2 Hooked; 1/2 Knobby tion. For the first cross they are limited 3. 1,1 x 2,2 All Knobby to selecting a male and a female from 4. 2,2 x 2,2 All Split the field population. Subsequent Downloaded from http://online.ucpress.edu/abt/article-pdf/58/8/478/47735/4450215.pdf by guest on 27 September 2021 5. 1,2 x 1,2 1/4 Hooked; 1/2 Knobby;1/4 Split crosses can be made with parentsfrom 6. 1,2 x 1,1 1/2 Hooked; 1/2 Knobby the field collection or from the various 7. 2,2 x 1,1 All Knobby offspring generations. Students can 8. 1,2 x 2,2 1/2 Split; 1/2 Knobby performas many crosses as they want 9. 2,2 x 1,2 1/2 Split; 1/2 Knobby and do statisticaltests as they generate 3These ratios are those that could be expected with large numbers of offspring. data and hypotheses about their popu- Students should be made aware that the outcome for any single cross may vary lation of organisms. from this ratio. Figure 2. A structurefor a codominanceproblem. Some Background Related to the Simulation From eight years of work with stu- Trait (Nose Shape) Male x Female Offspring dents solving GCK problems (Stewart Variations Females Males & Van Kirk 1991; Stewart, Hafner, 1. 1,1 x 1,1 Blue Johnson & Finkel 1992) I now realize Straight 10 6 2. 1,1 x 1,2 Blue how different solving effect-to-cause Curly 7 8 3. 1,1 X 2,2 Blue problems is for them. During this time Hooked 12 7 4. 2,2 x 2,2 Black many students have helped my col- 5. 1,2 x 1,2 3/4 Blue; 1/4 Black leagues and me develop ideas that help Figure 3. A Field Population Card for a 6. 1,2 x 1,1 Blue codominance problem. in the solving of genetics problems. 7. 2,2 x 1,1 Blue These ideas are listed below and then 8. 1,2 X 2,2 1/2 Blue; 1/2 Black described in more detail. 9. 2,2 x 1,2 1/2 Blue; 1/2 Black they perform crosses. The types of 1. Use a general genetics problem- cards necessary for a simple domi- Figure4. Types of OffspringCards for solving agenda. nance problem are shown in Figure 4 simple dominance. 2. Systematicallyexplore the search and examples of the cards are shown in space of the problem. Figure 5. Enough Offspring Cards will be needed so that a range of offspring Trait: Eye Color ratios could result from any particular Parents: Male: Blue Eyes cross of the same genotypes. By mak- Female: Black Eyes ing multiple cards for the same cross, Offspring: Male: 13 Blue Eyes students come to realize that offspring Female: 17 Blue Eyes ratios are probabalistic rather than de- terministic. It works well if the major- Trait: Eye Color ity of cards have offspring with pheno- Parents: Male: Blue Eyes Black Eyes type numbers that are within one or Female: 11 Black Eyes two of the expected numbers and a few Offspring: Male: 13 Blue Eyes; 17 Blue 14 Black Eyes in which the numbers are more ex- Female: Eyes; treme. When Offspring Cards have Color been produced it is useful if students Trait: Eye Male: Blue Eyes organize them similar to what is shown Parents: Female: Blue Eyes in Figure 6.
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