Fast Plants Stem Color Inheritance Study

ISEF Category: Plant Sciences

Subcategory: Genetics and Breeding  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A pea plant can look purple in one light and green in another, but the genes did not change. That split between genotype and phenotype is the heart of this project. You can test whether light changes the stem color ratios you expect from Mendelian inheritance. If the ratios shift, you have a real genetics question, not just a pretty plant.

What Is It?

This project looks at stem color in Wisconsin Fast Plants, a fast-growing version of Brassica rapa. Stem color comes from anthocyanin, a pigment that can make stems look purple. In simple Mendelian inheritance, you expect offspring to follow predictable ratios based on the parents' alleles, which are gene versions.

The twist is environment. Light can affect how much pigment a plant makes, so you are not just asking what genes are present. You are asking how strongly the environment changes what you see. Think of genes as the recipe and light as the oven setting. The recipe may stay the same, but the final cake can still look different.

Why This Is a Good Topic

This is a strong science fair topic because you can test a clear genetic prediction, then check whether light changes the visible outcome. You get real data, countable categories, and a clean comparison between expected and observed ratios. The project also connects to crop breeding, plant development, and how environment shapes traits. You can learn basic genetics, experimental design, and chi-square analysis without needing a university lab.

Research Questions

• How does light intensity affect the proportion of purple versus green Fast Plant stems??
• What is the effect of different light colors on anthocyanin stem expression in Fast Plants??
• Does changing photoperiod alter the observed stem-color ratio in Fast Plant offspring??
• To what extent do observed stem-color counts match the expected Mendelian ratio under each light condition??
• Which light condition produces the largest deviation from the expected stem-color ratio??
• How does one parent line versus another change stem-color inheritance under the same light treatment??

Basic Materials

• Wisconsin Fast Plants (Brassica rapa) seeds or starter kit.
• Small pots or planting trays.
• Potting mix or growth medium.
• Grow lights with adjustable distance or color settings.
• Timer or outlet timer for light scheduling.
• Ruler or caliper for plant height checks.
• Labels and a permanent marker.
• Digital camera or phone camera for documentation.
• Notebook or spreadsheet for counts and observations.
• Gloves and a tray for cleanup.

Advanced Materials

• Wisconsin Fast Plants (Brassica rapa) genetic lines with known stem-color traits.
• Controlled growth chamber or plant growth shelves.
• Light meter or quantum sensor.
• Spectrometer or colorimeter for pigment-related measurements.
• Imaging setup with fixed lighting and a color reference card.
• Stereo microscope for early phenotype checks.
• Analytical balance for sample prep if extracting pigment.
• Spreadsheet software or statistical software for chi-square and contingency tests.
• DNA extraction and PCR supplies if confirming genotype is part of the study.
• Environmental monitoring sensors for temperature and humidity.

Software & Tools

• Google Sheets: Organizes phenotype counts and calculates expected versus observed ratios.
• ImageJ: Measures stem color intensity from standardized photos.
• R: Runs chi-square tests and compares treatment groups.
• Python: Helps automate image analysis and summarize data.
• PubMed: Finds review articles and primary papers on anthocyanin and plant genetics.

Experiment Steps

1. Define the exact trait you will score, such as purple, green, or intermediate stem color.
2. Choose the genetic cross or seed source that gives you a clear Mendelian expectation.
3. Decide which light factor you will change first, such as intensity, color, or day length.
4. Plan your control group so you can separate genetics from environment.
5. Build a scoring method for stem color that stays consistent across all plants.
6. Choose a statistical test before you collect data so you know how you will judge the ratios.

Common Pitfalls

• Scoring stem color by eye under different room lighting, which makes the same plant look like a different phenotype.
• Mixing plants from different seed lots, which can blur the expected inheritance pattern.
• Using too few offspring, which makes Mendelian ratios look wrong just from random chance.
• Changing several light variables at once, which hides the effect of any one treatment.
• Recording only final color and skipping early growth checks, which can miss plants that never had a fair chance to express anthocyanin.

What Makes This Competitive

A stronger version of this project does more than count purple and green stems. You can compare expected and observed ratios with the right statistical test, then ask whether the same genotype behaves differently across light conditions. Strong projects also standardize photography or scoring, so the color call is not subjective. If you add a genotype check or a pigment measurement, you move from a simple inheritance demo to a sharper study of gene expression and environment.

Project Variations

• Test how stem-color ratios change across red, blue, and white light instead of changing only brightness.
• Compare two Fast Plant crosses, one with a clear purple-stem trait and one with a weaker color signal.
• Score stem color with standardized phone photos and ImageJ instead of only using visual categories.

Learn More

• USDA Fast Plants resources: Search for Wisconsin Fast Plants teaching materials and genetics guides on the USDA educational pages.
• PubMed: Search review articles on anthocyanin biosynthesis, light response, and plant phenotype.
• Mendelian Genetics textbook chapters: Find free introductory genetics chapters through university open textbooks or library previews.
• NIH genetics basics: Use NIH educational pages to review alleles, genotype, phenotype, and inheritance ratios.
• University OpenCourseWare plant biology lectures: Search MIT OpenCourseWare or similar university course pages for plant genetics and light signaling lectures.