Wisconsin Fast Plants® Monohybrid Crosses Inquiry
Life Science—Mendelian Genetics, Variation of Traits. Recommended for grades 9-12.
Teacher Prep: 30 min (Note: Seeds take 2 to 3 days to germinate.)
Student Activity: 30 min for germination setup on day 1; 10 min for days 2 to 4 for observation; 30 min on day 5 for observation and conclusions
Safety Goggles Recommended
ViewEssential Question
How can monohybrid crosses be used to predict the genotypes and phenotypes of the parent generation?
Investigation Objectives
- Observe phenotypes for the F2 generation of Wisconsin Fast Plants®.
- Identify the genotypes of the F2 generation plants.
- Use monohybrid crosses to predict the genotypes and phenotypes of the F1 generation, and then of both parents, P1 and P2.
Next Generation Science Standards* (NGSS)
Science and Engineering Practices
Developing and Using Models
- Students will develop a model of variation in traits for Wisconsin Fast Plants®. They will use their model to predict the phenotypes of F1 generation plants.
Disciplinary Core Ideas
LS3: Heredity: Inheritance and Variation of Traits
- LS3.B: Variation of traits among Wisconsin Fast Plants® will be determined through seed germination investigations.
Crosscutting Concepts
Patterns
- Observed patterns of traits in Wisconsin Fast Plants® guide organization and classification of trait variation. Relationships among inherited traits can be traced.
Safety & Disposal
Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Require students to adhere to all laboratory safety rules.
Dry plants out completely, place them in a resealable bag, and dispose of them in the trash. Plants may be allowed to continue to grow for additional investigations.
Procedures
- Place a filter paper or paper towel disk in the bottom of a petri dish. The paper should cover the dish's bottom.
- If you are using paper towels, cut them into disks to fit the bottom of the petri dishes prior to the activity. If the paper towels are thin, 2 layers may be necessary to keep the seeds moist.
- Space the 10 seeds out evenly on the filter paper.
- To save time, count out 10 seeds for each student or group before the activity.
- Use the spray bottle to moisten the seeds and paper. The paper should be damp, but not sitting in a puddle.
- Cover the petri dish and place it under a fluorescent lamp.
- Check the petri dishes. Make sure seeds are separated and moist, but not standing in water. Place all seeds under intense fluorescent light for the duration of the investigation. Seeds should germinate in 2 to 3 days.
- Observe the seeds daily for 4 or 5 days, or as directed by your teacher. Record your observations on the data sheet.
- Remind students to observe the seedlings carefully. They need to look at stem and leaf color. Color may change in intensity over time.
- Use the spray bottle to mist the seeds as needed. They should be kept moist, but not wet.
If students wish to perform the experiment they designed, have the additional seed packets available. The same germination technique may be used.
An alternative is to grow the parent generation through maturity and manually pollinate the parent plants, collect those seeds, and repeat the procedure for the F1 generation.
| Seed Stock (Item Number) |
Genotype | Phenotype | Notes |
|---|---|---|---|
| Purple Stem, Hair (158810) | ANL/ANL (dominant) YGR/YGR ROS/ROS EIN/EIN DWF1/DWF1 |
purple stem, sometimes extending to midribs of leaves; color varies from purple to dark pink | hair trait is quantitative and therefore best ignored in introductory activities |
| Non-Purple Stem, Hairless (158818) | anl/anl (recessive) | green stem | cross with 158810 for a monohybrid F1 |
| Yellow-Green Leaf (158843) | ygr/ygr (recessive) | yellow-green leaves, purple stems | cross with 158810 for a monohybrid F1, or with 158812 for a dihybrid F1 |
| Non-Purple Stem, Yellow-Green Leaf (158843) | anl/anl, ygr/ygr (double recessive) | yellow-green leaves, green stems | cross with 158810 for a dihybrid F1 |
| Rosette-Dwarf (158815) | ros/ros (recessive) | very short plant | internodes do not elongate |
| Tall Plant (158825) | ein/ein (recessive) | tall, spindly plant | abnormally tall due to elongation of internodes |
| Petite (15833) | dwf1/dwf1 (recessive) | reduced height | mature at 5-15 cm; normal is 17-20+ |
| Variegated (158820) | Var (non-Mendelian) | irregular leaf areas are devoid of chlorophyll | trait is part of the chloroplast genome, which is transmitted through the cytoplasm of the ovule; trait is not transmitted by pollen |
Data
Record the number of seeds germinated each day for 4 or 5 days, or as your teacher instructs. Identify the color of the stem for each seed germinated.
| Fast Plants® Seed Germination Data F2 Generation | |||
|---|---|---|---|
| Day | Number of Seeds Germinated | Purple Stems | Green Stems |
| 1 | |||
| 2 | |||
| 3 | |||
| 4 | |||
| 5 | |||
| Total | |||
Data will vary by group but should produce 75% purple stems and 25% green stems.
Analysis & Discussion
-
What are the 2 possible stem phenotypes?
Purple, hairy
Non-purple, hairless -
Calculate the ratio and percentage for each phenotype.
75% purple and 25% green
-
Using your data, which phenotype appears to be dominant? Why?
Purple, because of the greater percentage
-
For each stem phenotype, identify the possible genotypes.
Purple dominant, homozygous ANL/ANL and heterozygous ANL/anl
Green recessive, homozygous anl/anl -
Using a monohybrid cross, predict the phenotypes and genotypes of the F1 generation plants
ANL/anl × ANL/anl
ANL anl ANL ANL/ANL ANL/anl anl ANL/anl anl/anl Ratio of 3:1 purple to green given by the data, so both F1 parents were heterozygous purple, ANL/anl.
-
Using a monohybrid cross, predict the phenotypes and genotypes of the parent (P1 and P2) generation plants.
To produce heterozygous offspring, one parent must be homozygous dominant, ANL/ANL and the other must be homozygous recessive, anl/anl.
ANL ANL anl ANL/anl ANL/anl anl ANL/anl ANL/anl -
Design an experiment to test your predictions. (Check with your teacher about performing your experiment.)
Student answers will vary, but should include comparing phenotype counts for each generation of seeds. The specific phenotypes from each seed packet should be counted and compared to the ratios predicted by Punnett square crosses. The chi-square statistic may be introduced as an analysis tool now, since students will have actual seed phenotype data.
If time permits, you may begin with the P1 and P2 seeds and cross-pollinate the plants in class, harvest the seeds (F1 generation), and germinate those seeds. The same procedure can be used to test the crossing of F1 plants to identify F2 phenotypes and genotypes. This procedure will take several weeks.
*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products.
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