Mendelian Genetics in Wisconsin Fast Plants

Background

Throughout my life I have always been interested in biology and have thought about conducting scientific research in my future. The STEM Research Mentorship Program offered me a great opportunity to be introduced to research and explore something that I am interested in. In the AP Biology class at CCHS last year, I learned much about genetics and gene expression. I wanted to work with living specimens during this research project, but also wanted to be able to work independently and conduct research at my own home. Wisconsin Fast Plants allowed me to do both of these things as well as explore topics that I have learned.

Wisconsin Fast Plants: A Model of Genetics and Gene Expression

Rapid-cycling Brassica rapa, also known as Wisconsin Fast Plants, are used often in genetic research due to their short life cycles. These plants have lifespans of around 40 days and express traits extremely quickly, making them highly valuable when studying the inheritance and expression of genetic traits. During this experiment, I focused on the inheritance and expression of two traits: leaf color and stem color. Wisconsin Fast Plant leaf color is controlled by the ygr/ygr gene, with green coloration being dominant. Stem color is controlled by the anl/anl gene, with purple color being dominant.

Life Cycle

Plants approximately 4 days after planting

Plants approximately 10 days after planting

Plants approximately 25 days after planting

Plants around 50 days after planting (seed pods developed)

Wisconsin Fast Plants typically can complete a full life cycle and produce seeds within 40-45 days. Seedlings emerge 1-2 days after seeds are planted, first having two distinct embryonic leaves or "cotyledons." Soon after, plants begin to develop their "true leaves," which are much larger. Buds emerge alongside these true leaves and they usually flower within 14-15 days. Pollination is most effective when done 1-2 days after flowers first open, and seed pods take around 20 days to fully mature. During my experiment, I harvested seed pods by cutting them off when they were ready and sealing them in plastic bags for at least seven days or until they appeared dry and brittle. Once seed pods were dried, I could easily remove the seeds by cutting an opening in the seed pods and gently removing the seeds.

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Pollination

During this video, I recorded the process of pollinating two Wisconsin Fast Plants. This was the first pollination I performed. This video also gives some insight into the experimental setup. In order to provide them with as much light as I could from my home, I grew the plants under two lights within close proximity to them as well as close to a window. Plants were grown by placing growing quads on top of a water mat that led to a water reservoir underneath.

Pollinations were performed by creating beesticks - that means gluing dead bees to sticks and using them to transfer pollen between plants. Because this is how pollen is transferred in a natural environment, it was the most effective way to pollinate plants.

Results & Discussion

Although I initially intended to breed more generations of plants, the life cycles of my plants ended up being longer than expected, with them taking nearly 30 days, sometimes more, to flower rather than the expected 14. This posed another research question: to what extent did environmental factors in which the plants grew affect their life cycle? In order to complete my project in the allotted time frame, the first group I planted grew throughout the winter. To my surprise, this group was greatly affected by the cold outside temperatures and decreased sunlight. Many of them became "spindly," meaning they grew very tall and thin, and had shorter leaf length than they typically would. Conversely, another group of plants that I planted nearly a month later on February 13th were shorter, less spindly, had larger leaves, and had thicker seed pods.

Plant Height & Leaf Length

At the end of their life cycles, I took a sample of plants from each group by cutting them at the roots and measuring their height and leaf length. While there was a visible difference between the two groups, I conducted statistical analysis using standard error of the mean and found that there was no significant difference between the two groups regarding height and leaf length. However, this hypothesis could be explored further using a larger sample size of plants, which could produce more clear results.

Genetics

Through the genetics experiments I conducted, I was able to make predictions and observations about the genotypes of the plants. For instance, one pollination I conducted was between two plants, one with purple stem and yellow-green leaves (ygr/ygr), and one with green stem and green leaves (anl/anl). The two seeds produced by this type of pollination ended up producing two plants, one with a green stem and one with a purple stem. In order for the green stem to occur, the plant with the ygr/ygr genotype for leaf color likely had an ANL/anl genotype for stem color. However, this cannot be verified from such a small sample size and the research would have to be continued with a larger sample in order to say for sure.

F1 x F1 Offspring

Two seedlings from an F1 x F1 pollination I performed ended up germinating. One seedling has a purple stem and yellow-green leaves (ygr/ygr), and one seedling has a green stem (anl/anl) and green leaves.

Punnett Square

The Punnett Square created for this pollination helps explain the phenotypes of the offspring. The purple highlighted genotypes correspond to the purple seedling, and the green highlighted genotypes correspond to the green seedling.

What I Learned

This research project was definitely more difficult than I was expecting, and there were some obstacles along the way. As I mentioned earlier, for instance, I planted most plants in the middle of winter. This led the plants' life cycles to be longer than expected, and I did not get all of the results I wanted. Regardless, I learned so much from this project. I learned many research techniques and I gained independence in my pursuit of research as I grew the plants at my home. Most importantly, I learned that you must have an open mind when doing research, especially when working with living specimens. Living organisms can be difficult to control, and when something does not go your way, you must be able to adapt. I feel that this project was a great opportunity for me to prepare for my future.

As a final product, I wrote a lab relating to my studies that could be used by a biology class. I will introduce the lab to a biology teacher at my school in hopes that it might either be used or that the teacher can gain some ideas or inspiration from it. To explore the lab, click on the document below.

Mendelian Genetics in Wisconsin Fast Plants Lab for Biology Class

Interview - Briana D.mp4

Interview

Join Briana and Dr. Nguyen for a conversation about the lessons learned throughout this project!

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