Vanderveer
Biology 2012
Genetic Probability1
Grade Level: 9-12
OBJECTIVES:
MATERIALS:
PROCEDURE:
1. Distinguish expected and observed genetic ratios.
2. Demonstrate that in genetic crosses, as the number of offspring
increases, the difference between observed and expected results
decreases
3. Demonstrate the practical applications of genetic probability
Each group needs:
 2 boxes
 100 red beans
 100 white beans
 calculator
1. Students should be divided into groups of 2. (Preferably their table
partner)
2. Before materials are handed out, expected ratios should be
determined on paper via Punnett square (R=red; r=white). A
heterogeneous cross is demonstrated below:
3. While students are collecting their materials, explain that each box
represents a parent organism and each bean an allele. Each box
should have 100 beans. Red beans represent the dominant allele
while white represent the recessive (R=red; r=white).
4. The teacher begins the activity by placing the genotype of the parents
on the board. Each group will count out the appropriate number of
each bean per box: RR=100 red beans; Rr= 50 red and 50 white
beans; rr= 100 white beans.
5. The teacher now times the class for one minute during which one
student will pull one bean from each box while the other tallies the
results. At the end, they will calculate the observed ratio for each
cross.
6. While each group calculates their ratios, the teacher will collect data
and compile class ratios. Calculation of ratios will be as follows:
RR=A, Rr=B, rr=C.
A+B+C=D, D/4=E.
A/E=1st ratio; B/E=2nd ratio; C/E=3rd ratio.
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Unit: Genetics
Vanderveer
Biology 2012
7. Have students compare group ratios, class ratios, and the expected
ratios. Then have each student submit an answer to the following
question: which are closer to the expected ratio and why?
1.
Adapted from Teachnology at http://mypages.iit.edu/~smile/bi8602.html
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Unit: Genetics