This investigative case module was prepared as part of a BioQUEST faculty development workshop. The cases, resources, and implementation strategies were developed by participants for use with their own students. We invite you to adopt and adapt the following materials.

The BioQUEST Curriculum Consortium is committed to the reform of undergraduate biology instruction through an emphasis on engaging students in realistic scientific practices. This approach is sometimes characterized as an inquiry driven approach and is captured in BioQUEST's three P's (problem-posing, problem-solving, and peer-persuasion). As part of this workshop groups of faculty were encouraged to initiate innovative curricular projects. We are sharing these works in progress in the hope that they will stimulate further exploration, collaboration and development. Please see the following links for additional information:

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Investigative Cases
The Case: My Twin Sister

Scenario: The Letter  

Dear Aunt Laurie,
Great news, school’s out and summer vacation is here.

How’s medical school? I bet those little kids just love you as their doctor.

Well, I guess you heard the news... I’m going to have a baby sister in July. I can’t wait!! I think all of us will be really happy to have a new baby. They’re so cute. 

This has really been a crazy couple of years with a lotta ups and downs.
First, Mother is killed by a drunk driver, then Daddy won’t talk for weeks-
so Aunt Joy comes to take care of me. Boy is that weird! Your Mother’s
identical twin makes you feel like you’re seeing a ghost every morning at
breakfast. Up and down up and down. Then the BIG SURPRISE :-o
Daddy marries my aunt, mother’s twin!

I wonder, is she my step-mother, my aunt or my twin-mother? So when this new baby comes, will she be me? or a step-me or an identical twin me?

Answer ASAP- cause this is a genuine serious problem.

In the twilight zone, 

Case Author:
Eloise Carter Emory University:Oxford College

Case Analysis

Will Millie be identical to her baby sister? Why or why not?

What processes are involved in the formation of gametes and how do they affect genetic variation?

Option: Include a know / need to know chart like the one below:

What do you know?
What do you need to know?

Learning Goals


Students completing this module will be able to:

  • Describe the steps in meiosis
  • Describe the products of meiosis
  • Describe the structure of chromosomes
  • Explain how meiosis promotes genetic variation
  • Explain how fertilization contributes to genetic variation



Investigations and Activities

  • Students will be given the case scenario in class. 
  • Working in groups of 4, students will research and answer the questions generated by the case using text and other resources provided by the instructor. 
  • Students will discuss possible responses to Millie’s letter.

    Classroom to Lab Activities:

  • Students must thoroughly review the stages of meiosis using the lab manual and bead kits. 
  • They will prepare 5 critical questions about meiosis.
  • In lab they will assume the role of "Aunt Laurie" or "Millie."

    Laboratory Investigations:

  • Students will draw for the role of "Aunt Laurie" or "Millie". 
  • "Aunt Laurie" will teach "Millie" the steps of meiosis using the bead model and the laboratory exercise as a guide.
  • "Millie" will ask 5 critical question to try to stump "Aunt Laurie."

    Demonstrations and Computer Investigations

  • Students will observe human chromosomes with microscope slides
    and karyotypes on demonstration.
  • Students can use imaging software on web to investigate chromosomal mutations.



Biology textbooks and diagrams - to respond to Millie’s letter: 

Laboratory Exercise: "Mitosis and Meiosis", Judith Morgan, Concepts in Biology Laboratory Manual.- laboratory investigation using bead model and demonstration of chromosomes - includes an investigation of chromosome mutations, including karyotypes for 4 patients with different syndromes.
Information on meiosis, chromosome structure and genetic variation. Site uses lily for the example of meiosis. The active tutorial is terrific, including questions, answers, photomicrographs.  Animation of chromosomes, runs 4 times with some notes. One of many sites with information on identical twin studies that deal with environment vs. genetics. This may be useful for thinking about identical twins.

Students will usually obtain additional references or resources
to help answer or explore their questions.

Special Data Items

1. twin_s1.gif
2. twin_s2.gif
3. twin_s3.gif
4. twin_s4.gif
5. twin_s5.gif
6. twin_s6.gif


Student Products

Students will write a letter to Millie answering her questions about the genetic similarity with her baby sister. The letter should include an explanation of the role of meiosis and fertilization in genetic variation.

Students will turn in a copy of their 5 "Millie" questions.

Assessment and Evaluation Plan

Letter to "Millie" -  20% 

5 "Millie" questions - 20% 

Peer evaluations - 10%

Lab examination - 50%



Course name:
Introduction to Biology
Likely sequence in syllabus:
Beginning of Genetics
Time during term:
one week
lecture / lab
Students in course:
mixed majors/non-majors
Collaborative elements:
Small Groups
Additional notes:




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