Materials Included In Kit

Additional Materials Required

Safety Precautions

This activity is considered non-hazardous. Have students wash their hands thoroughly after handling the tobacco seeds.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Materials can be separated and disposed of following Flinn Suggested Disposal Method #26a. Petri dishes can be washed and reused.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. The initial setup can be completed in half of a 50-minute class period. Additional partial class periods must be spent checking and watering the seeds and collecting the data.

• Green is a dominant trait to albino in tobacco leaves. The parents of the tobacco seeds used in this experiment were both heterozygous for green/albino. An expected ratio of 3:1 (green:albino) is therefore predicted. A ratio of approximately 3:1 will result with the seedlings grown in the light environment. In the dark, however, the genotype cannot express itself due to the lack of light necessary for chlorophyll production. The seedlings will all look albino when grown in the dark. When placed in the light (after being in the dark) the phenotype will quickly change to green in those seedlings possessing the gene for green. This restores the predicted 3:1 ratio.
• Reversing the environment of the seedlings first grown in the light (and then placed in the dark) will likely not reverse the ratio very quickly. Given several days in the dark, however, the seedlings will all become achlorophic and all look albino.
• Albino can be a deceptive word for students. When recording data you might describe them as green and non-green since the albino seeds might actually have a light green tint.
• Be sure the seedlings are kept moist while they are germinating. When watering the seedlings in the dark, be sure students do it quickly and with minimal exposure to light.

Sample Data

Chart 1. Before Reversal

Answers to Questions

1. If the parents of the tobacco seeds used in this experiment were heterozygous for albino (green being dominant), what ratio of green to albino would you expect in this generation of tobacco plants? Did the expected ratio result? In the light? In the dark?
   

   A ratio of 3 green to 1 albino is expected. Answers may vary but a ratio approaching 3:1 is likely in the light but nearly zero in the dark.
   

2. How do you explain what happened when you reversed the environmental conditions?
   

   The genetically green tobacco produced chlorophyll in the light and they turned green. The green tobacco in the light turned lighter to albino when placed in the dark.
   

3. Defend which is most important for tobacco seedlings—its heredity or its environment. Use your data to help defend your answer.
   

   Defenses will vary but both factors can be defended as critical for the life of a tobacco plant. Genetics are very pervasive, but only if the environment allows the genetic expression to occur.

Introduction

Why are people the way they are? Is it a result of nature (genetics) or nurture (environment)? What about in plants? Discover the balance between heredity and environment in determining the traits of an organism.

Concepts

• Heterozygous

• Dominant vs. recessive
• Genotype
• Phenotype

Materials

Safety Precautions

This activity is considered non-hazardous. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Label the bottom of one Petri dish “light” and the bottom of another Petri dish “dark.” Include your name and date with the label.
2. Place a piece of filter paper into the bottom half of each of the two Petri dishes. If necessary, trim the paper with a scissors so that the paper lays flat in the bottom of the dishes.
3. Soak the filter paper with tap water using a pipet. Drain any excess water that is not absorbed into the paper.
4. Sprinkle 25 tobacco seeds evenly over the moistened filter paper in each of the two Petri dishes. Be sure the seeds are spread out evenly in the dishes.
5. Replace the covers on the two dishes. Place the dish labeled “light” in a well-lit area (e.g., greenhouse, window area, under lights) as directed by your teacher. Place the dish labeled “dark” in a completely darkened area where it will receive absolutely no light. (This could be in a drawer, closet, or under a lightproof box or cover.)
6. Allow the seeds to germinate for one week. Let the dishes sit undisturbed except to add water if the filter paper should become dry. If the dish in the dark needs added water, add it quickly and in a reduced light environment.
7. Observe the Petri dishes at the end of one week. Some seedlings will be pale in color (albino) with little or no green pigment. Other seedlings will have green areas forming. When nearly all the seedlings have germinated, count each seedling as either green or albino. Record your results in Chart 1 on the Heredity and Environment Worksheet.
8. After making your counts of “light” and “dark” seedlings, reverse the location of the Petri dishes for 2–3 days. Place the “light” dish in the dark and the “dark” dish in the light.
9. After several days observe the Petri dishes again and record the number of each kind of seedling in Chart 2 on the Heredity and Environment Worksheet.
10. Answer the questions on the Heredity and Environment Worksheet.

Student Worksheet PDF

10330_Student1.pdf