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How Does Chance Influence Inheritance?

Frank Castillo
1994 Woodrow Wilson Collection


Objectives:

a) to observe how chance affects which genes appear in gametes (Mendel's Law of Segregation)

b) to use beans to represent the recombination of alleles during fertilization

Materials:

  • two containers (soup cans, pint milk cartons or similar containers)
  • one hundred red beans
  • one hundred white beans
  • Student Work Sheet:

    The students should sit in pairs for this activity. Each cooperative team should receive a set of materials, with each container holding a mixture of fifty red beans and fifty white beans. The students are to complete the lab and answer the accompanying questions:

    1. If each container represents a set of genes from one parent, what could each bean really represent? _________________________________________________________

    2. Take one bean from each box at the same time, and lay the pairs in rows assigned: red-red, red-white, white-red and white-white. Why must a bean be chosen from each box? _________________________________________________________________

    3. After each drawing from the containers, count the beans in each row and record the selected combinations in the table presented below. _________________________________________________________________

      How many combinations are possible using two kinds of beans? ______________

      What accounts for the variation in offspring represented by the pairs of genes? ___________________________________________________________________

    NUMBERS OF PAIRS OF BEANS IN:
    RED-RED RED-WHITE WHITE-RED WHITE-WHITE TOTAL
    Trials
    #1
    #2
    #3
    #4
    #5
    #6
    #7
    #8
    #9
    #10
    #"
    #"
    #"
    #100

    Summary And Conclusion:

    You can discover the actual ratios for each type of gene pair using these calculations with the following procedure:

    You would expect to have 25; 25; 25; 25 for each gene pair combination, if you were drawing from the 100 beans in the container. What was you percentage of combinations for each pair? Ask your teacher if these were consistent with what was expected.

    Questions:

    1. Why is it necessary to have so many beans in each container? ___________________________________________________________________
      ___________________________________________________________________

    2. Why is it necessary to select so many pairs? ___________________________________________________________________
      ___________________________________________________________________

    3. What are the chances of selecting a gene pair with the same color? ___________________________________________________________________
      ___________________________________________________________________

      With a different color? _______________________________________________

    4. What genetic principles have you discovered by this activity? ___________________________________________________________________
      ___________________________________________________________________

    5. How does chance selection of genes, as shown with this bean lab, provide the basis for variation in organisms? ___________________________________________________________________
      ___________________________________________________________________

    Bibliography:

    Otto, James, Albert Towle, David Otto and Myra Madnick. 1977. Biology Investigations. Holt, Rinehart and Winston Publishers.

    Teacher's Information:

    I use this lab to implement the presentation of Mendel's work and theories. The class is structured as follows:

    1. class introduction to theories, vocabulary words and historical background of Gregor Mendel's work with pea plants.

    2. reading and discussion of the lab activity with the class.

    3. implementation of activity.

    4. students work on questions in cooperative teams following completion of activity.

    It is recommended that the teacher maintain an effective sense of discipline in the classroom so as to avoid off-task behavior, i.e. students throwing beans around the class. It is important to pair up one capable student with one who has difficulty in understanding concepts. The activity is not difficult for students to complete and it serves as a "hook" for new information in subsequent chapters on genetics. I would also suggest that the teacher continually walk around the class to monitor student activity and assist whenever needed. This assures them that you are helpful in their completing the activity.

    Students should understand the following vocabulary words:

    homozygous incomplete dominance
    heterozygous allele segregation
    recessive trait P, F1, F2 generations
    dominant trait lethal genes*

    * this could be developed as an issue related to sickle-cell disease, cystic fibrosis, etc., with emphasis on an individual who is a carrier and one who has the disease expressed.


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