Peppered Moth (Biston Betularia) Lab

Peppered Moth ( Biston betularia ) Lab

Introduction: The peppered moth is a light-colored moth with gray spots, which was common in England in the 1800s. (Occasionally, people would find peppered moths with dark gray, but those where less common.) The peppered moth lives its life in the woods trying not to be eaten by the birds. Around 1850, people noticed that the darker moths began to be more common, usually in areas near coal burning factories. Burning coal produces lots of sooty black smoke. Our job today is to run a simulation to discover why this happened.

Materials: White background paper = trees with white bark Newsprint background paper = trees with darkly colored bark Small white squares = lightly colored (white) peppered moths Small newsprint squares = dark gray peppered moths

Roles: Bird – One group member’s finger will simulate the birds’ beaks. Birds must squint so that their vision is not 100%. Timer – Times feeding period (15 sec). Recorder – Records numbers of surviving moths (how many white squares are left and how many newsprint squares are left.) Reproducer – For each square left at the end of the feeding period add another matching square to the background (example: if 3 white squares are left, then the reproducer adds 3 more white squares). Everyone – Copy the chart below on your paper and make sure to include 5 rows for 5 generations (this one only shows two).

Population of peppered moths in England in the 1800s Generation # of light # of dark # of uneaten # of uneaten moths at start moths at start light moths dark moths of gen. of gen. (survivors) (survivors) 1 2 etc.

Simulation Instructions: England in the 1800s 1. Lay out the white background to represent the white tree bark found in the early 1800s in England. 2. Reproducer sprinkles 30 white squares and 10 newsprint squares randomly in a thin layer (DON’T LOOK BIRDS). 3. Timer says when to start and times bird feeding for 15 seconds. Bird must only pick up one moth at a time during feeding period and remember to squint so your vision is not perfect. Each feeding period of 15 seconds represents one generation. 4. At the end of this feeding period the recorder records the number and colors of remaining moths in the background (the survivors). 5. Reproducer doubles the survivors of each color. Recorder now records this number as the beginning of generation 2. 6. Repeat this process through five generations or until only one color remains in the surviving population. Don’t forget to record! Coal Burning Factories are Built Nearby: 1850s 7. Now you will change the background to the newsprint to represent the soot- stained bark of 1850s England. 8. Everyone draw a table similar to the one on the front and title it, “Population of Peppered Moths in England in the 1850s.” 9. Reproducer sprinkles 30 white squares and 10 newsprint squares randomly in a thin layer (DON’T LOOK BIRD) 10. Repeat steps 3-6 above. Don’t forget to record!

Graphing Data: Everyone! – Create a line graph of your data. The x-axis will represent generations and the y-axis represents the number of moths present at the beginning of each generation. Use two different colors to represent each of the different backgrounds (White trees data in 1 color, and dark tree data in another color- with a total of 4 lines when you finish.)

Discussion Questions: 1. Describe the population of peppered moths in England in the early 1800s. How many of each color were present? 2. Why did the number of dark moths increase in the 1850s? 3. What changed first, the environment or the incidents of dark moths in the peppered moth population? 4. Assume that moth color is determined by two alleles. If gray is the dominant phenotype then what are the two possible genotypes for gray color (use P and p)? 5. If the white phenotype is recessive then what is the genotype? 6. Even though white is recessive why was this color more common in the peppered moth population of the 1800s? 7. Most coal burning factories today “scrub” the smoke (catch the particles of soot) before it leaves the smoke stack. What do you predict has happened to the moth population since factories began doing this?