PUNNET SQUARE COIN TOSSING LAB

An exercise in probability . . .
DETERMINING THE GENOTYPIC AND PHENOTYPIC RATIOS
OF POTENTIAL OFFSPRING . . . THROUGH THE FLIP OF A COIN!

So what about Mendel . . .
By the way, how random is a coin toss, anyway?

Mr. Lazaroff's Biology

I. PURPOSE: To demonstrate the laws of probability, and the ratios of potential offspring, given specific sets of parents.

II. HYPOTHESIS: If I keep accurate records, then I will collect data that closely reflects the ratios predicted through the laws of probability.

III. EXPERIMENTAL DESIGN:

   A. MATERIALS:

1. Two coins (preferably not of the same type, so as to avoid confusion)

   B. PROCEDURE:

1. Assign letters, as instructed, to heads and tails of each coin.

• Trial 1 - BB x BB Coin 1: Heads = B, Tails = B
              (Parents) Coin 2: Heads = B, Tails = B
• Trial 2 - bb x bb Coin 1: Heads = b, Tails = b
              (Parents) Coin 2: Heads = b, Tails = b
• Trial 3 - BB x bb Coin 1: Heads = B, Tails = B
              (Parents) Coin 2: Heads = b, Tails = b
• Trial 4 - BB x Bb Coin 1: Heads = B, Tails = B
              (Parents) Coin 2: Heads = B, Tails = b
• Trial 5 - Bb x bb Coin 1: Heads = B, Tails = b
              (Parents) Coin 2: Heads = b, Tails = b
• Trial 6 - Bb x Bb Coin 1: Heads = B, Tails = b
              (Parents) Coin 2: Heads = B, Tails = b

2. Flip each coin simultaneously and record the appropriate letters for the pair of coin tosses (in Chart # 1; click HERE to print a copy); be sure to note whether or not the letter is underlined. (e.g. Toss 1 = BB) This will be useful in demonstrating that more than one combination of chromosomes can produce individuals with the same genotype

• Note: Each coin = one parent (the alleles of that parent)
• Heads & Tails = each possible gamete for that parent
• Heads = one allele for that gene
• Tails = the other allele for that gene
• Heads & Tails = on homologous chromosomes
• Heads = one chromosome in a homologous pair
• Tails = the other chromosome in a homologous pair
• The pair of letters you record = the genotype of a potential child of the two parents in that trial

3. Repeat step # 2  19 more times, for a total of 20 tosses in each of the six trials = 120 tosses in all
4. Add up the totals for each of your group's trials and calculate the genotypic and phenotypic ratios for each trial (Group Ratios in Chart # 1click HERE to print a copy).

Genotypic Ratio - # BB : # Bb : # bb
Hint: BB and BB and BB and BB = BB
Phenotypic Ratio - # Dominant : # Recessive
Hint: Dominant = BB or Bb, Recessive = only bb

5. Write the total results for each of the 6 trials on the chalkboard, and record the results for all of the groups in a class chart (Click HERE to print a copy.).  (I will give your group a number.)
6. Add the totals for each trial in the class chart (Click HERE to print a copy.), then calculate the genotypic and phenotypic ratios for each of the class trial totals (Class Ratios in Chart # 2; click HERE to print a copy).
7. Construct a punnett Square for each of the six trials and write the genotypic and phenotypic ratios for each square (True Ratios).

Hint: Use the parents indicated for each trial in step # 1.

8. Graph the Class totals (Not the ratios!!) for each of the six trials; this is easier to see if it is done as six separate graphs, side by side, on one page. ALL GRAPHS MUST BE HAND DRAWN! This is to ensure that I know that you know how to make a graph, rather than having the computer make it for you!

IV. DATA:  You will need to follow these links to print both Chart # 1 and Chart # 2.
 

NOTE: If you miss the lab, you can get a copy of the Lab Data on the eChalk.

1. Your group chart (Chart # 1; click HERE to print a copy) to show the results (genotypes) of all 20 tosses (children) for each of the six trials in your group.
2. The genotypic and phenotypic ratios for each of the trials in Chart # 1 (Click HERE to print a copy).
3. A class chart (Chart # 2; click HERE to print a copy) to show the results of each of the six trials for all of the groups in the class.
4. The genotypic and phenotypic ratios for each of the trials in Chart # 2 (Click HERE to print a copy).
5. The six possible punnett squares as indicated in step # 1 for each trial.
6. The genotypic and phenotypic ratios for each of the punnettt squares.
7. A graph showing the class totals for each of the six trials, all on one bar graph (i.e., 220 : 0 : 0, 0 : 0 : 220, etc.).
                        ALL GRAPHS MUST BE HAND DRAWN!

	BB x BB		bb x bb		BB x bb
Genotypic Ratio	BB : Bb : bb		BB : Bb : bb		BB : Bb : bb
	____ : ____ : ____		____ : ____ : ____		____ : ____ : ____
Phenotypic Ratio	Dominant : Recessive		Dominant : Recessive		Dominant : Recessive
	_____ : _____		_____ : _____		_____ : _____
	BB x Bb		Bb x bb		Bb x Bb
Genotypic Ratio	BB : Bb : bb		BB : Bb : bb		BB : Bb : bb
	____ : ____ : ____		____ : ____ : ____		____ : ____ : ____
Phenotypic Ratio	Dominant : Recessive		Dominant : Recessive		Dominant : Recessive
	_____ : _____		_____ : _____		_____ : _____

V. QUESTIONS:

1. How close were your group's ratios for each trial to the ratios of the class as a whole? Be specific.
2. How close were the class ratios for each trial to the ratios predicted by each of the punnett squares? Be specific.
3. Were any of the individual group's results extremely different from the ratios predicted by the punnett squares? Give a specific example and compare the ratios.
4. What does the data say about sample size and the accuracy of calculating ratios? Explain.

Compare your Sample Size with that of Gregor Mendel . . .

5. Can you, with confidence, predict the actual genotypic outcome for any one given toss of the coin in trial 6? Trial 4? Trial 3? Explain.
6. Can you, with confidence, predict the actual phenotypic outcome for any one given toss of the coin in trial 6? Trial 4? Trial 3? Explain.
7. If BB = BB = BB = BB, why did I have you indicate whether or not the B came from the heads or the tails (i.e., what does the underlining indicate in terms of chromosomes?)?
8. Define the following: P generation, F₁ generation, F₂ generation. Indicate which ones are used in the lab above. Use specific examples.

VI. CONCLUSION: You should know what to do! If you DON'T, click here!

This must be 1/2 page minimum. Discuss everything you learned in today's lab. Be sure to discuss possible errors in accuracy, and any ways to improve this lab. Be sure to include any additional questions triggered by this lab, and propose ways to test those questions in an additional experiment. Note: I don't want you to waste any of the 1/2 page discussing whether or not you enjoyed the lab; your discussion here should be purely of a scientific nature.

Mr. Lazaroff's Biology Classes
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