Introduction / Background
This case is based on a true story of a woman whose children were almost taken from her because her DNA profile indicated she was not the mother of her children.1 The interrupted case study follows the woman, her lawyer, and a research biologist as they try to determine why her DNA profile does not match her children’s profiles. As they learn about this very unusual case of genetic chimerism,2 students review information about the normal process of reproduction and genetic transmission in humans, form and evaluate hypotheses about the case, and are challenged to think about the possible implications of abnormal transmission of genes.
This case is used in the second semester of a two-semester sequence of biology classes for non-majors. It was designed to help students review meiosis and the transmission of genetic information learned in the first semester in preparation for discussion on the reproductive system, reproductive hormones, fertilization, and embryonic development. The case could be expanded for use in a biology class for majors or a genetics class.
Objectives
Review the genetic and cellular processes of human reproduction. Specifically, students review the formation of gametes, meiosis, transmission of genetic material, conception, and early development. While reproduction seems to be fairly interesting to most students, the molecular and genetic events are made more interesting in an exceptional circumstance such as chimerism.
Evaluate hypotheses about how a seemingly impossible event (a mother whose DNA does not match the DNA of her children) might occur given knowledge about how reproduction normally occurs. One of the overall objectives for my students in learning biology is to learn the process of science, in which known information is used to make hypotheses and form an understanding of new information.
Challenge students to connect the information from this case to other possible scenarios in which chimerism may be relevant.
Classroom Management
Students are asked to form groups in which to read and discuss each part of the case. They are told they will not have to hand in written answers to the questions, but will need to answer the questions and participate in class discussion for a grade. The first two parts of the case fit into a one-hour class period. The discussion of Part III, the epilogue, takes about 30 minutes of another class period. The epilogue can be used either in the class period following the discussion of the first two parts of the case, or several periods later after the biology of human reproduction is covered.
Part I – A Distraught Mother
In answering the questions associated with Part I of the case, students will immediately begin to try to figure out what is happening in this unusual case. They will need to be reminded to really look at how the normal process of gene transmission occurs. Students may conclude that Lillian’s story is impossible. Students also need to be reminded to evaluate the hypotheses put forward by the welfare people, which suggest that the children may be related to Lillian. The hypotheses are not formally stated in the case; however, they are implicit in the dialogue and the description of Damian’s discussion with Lillian. (A listing of these hypotheses is included in the Answer Key.) Some hypotheses that the students come up with may be inconsistent with the children appearing to be related to Lillian. For instance, students may suggest that the children were adopted. While this hypothesis explains why the children do not share DNA with their mother, it does not explain why they share DNA with their father or why they appear related to Lillian, unless Lillian (perhaps informally) adopted the children of Dwayne and one of her relatives.
For Part I, allow 15–20 minutes for small groups of students to read the case and come up with answers to the discussion questions. Whole class discussion of the answers will take around 15–20 minutes.
Part II – A Strange Child
Most students are surprised that chimeras and hermaphrodites exist. Students may have questions about whether hermaphroditism is caused by a genetic mutation, a disease, or some other known cause. Students are asked to come up with a way to test the hypothesis that Lillian is chimeric. For students who suggest DNA testing of her ovaries, I point out that this would require surgery, and ask them to think of less direct methods of getting the same information.
For Part II, allow around 10 minutes for small groups of students to read the case and come up with preliminary answers to the questions. Whole class discussion of the questions should take 10–15 minutes.
Part III – Epilogue: But How Does It Happen?
After letting the students read the epilogue in Part III, tell students about the true story on which this case is based, and show them the cover pages of journal articles reporting cases of hermaphoditism and chimerism.3,4 This case is based on the story of Lydia Fairchild, a woman whose children were almost taken from her because her DNA profile indicated she was not the mother of her children. She retained custody of her children, based on evidence that she may be genetically chimeric. Her story has been told in the documentary “I Am My Own Twin,” which has been posted on YouTube. She also has a website: http://www.geocities.com/mylifewithchimera/4.html
Students may have difficulty formulating more than one hypothesis about how chimeric individuals are formed. However, as being stumped is often part of scientific investigation, I feel it is still reasonable to ask them to try. Scientists are currently unclear as to how chimeric embryos occur naturally,5 and some students are disappointed that there is currently no good explanation for the mechanism of chimerization. Students fairly quickly come up with possible legal implications of this case.
The epilogue can be used in the class period immediately following the presentation of the first two parts of the case, or as a way to wrap up a chapter on reproductive biology. Allow around 10 minutes for small groups of students to read the epilogue and come up with answers to questions. Whole class discussion should take 10–15 minutes.
See the Modifications section below for an alternate epilogue that has students read a paper published in Science magazine and then answer a different set of questions.
Modifications for Use in Classes for Biology Majors
This case could be used in classes for biology majors. For a general biology class for non-majors, the case can be used without modification. For a genetics class or other upper level biology class, I have attached an alternate epilogue to these teaching notes. The alternate epilogue asks the students to read the primary research article that Dr. Vijayverigia refers to in the dialogue of Part II.6 While students will probably not understand all of the techniques mentioned in the article, the introductory paragraphs and concluding paragraphs should be mostly understandable. The article is a good example of how evidence is used to evaluate alternative hypotheses. It may be worth noting that the article was published in 1980, before the widespread, routine use of DNA for forensic identification. The potential implications of chimerism for DNA evidence apparently were not appreciated until cases appeared, such as the one reported by Yu, et al.7
Editor’s Note
Readers of this case will also be interested in Jessica Hutchison’s case titled “Giving Birth to Someone Else’s Child? A Case of Disputed Maternity,”8 also published in the case collection of the National Center for Case Study Teaching in Center. Both cases deal with genetic chimerism. While the cases are similar, Hutchison’s case presents more evidence than this case and presents that evidence in a series of parts. The evidence in Hutchison’s case comes in the form of HLA typing, whereas in this case the evidence is stated in terms of % similarity of DNA. The importance the instructor places on understanding techniques and interpreting primary data should be considered when choosing between the two cases.
Answer Key
Answers to the questions posed in the case study are provided in a separate answer key to the case. Those answers are password-protected. To access the answers for this case, go to the key. You will be prompted for a username and password. If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online or write to answerkey@sciencecases.org.
References and Notes
1 See the following websites for the story of Lydia Fairchild, on whose story this case is based:
“She’s Her Own Twin: Two Women Don’t Match their Kids’ DNA—It’s a Medical Mystery.” http://abcnews.go.com/Primetime/story?id=2315693 Last accessed: May 19, 2009.
The Discovery Health channel documentary, now on YouTube: I Am My Own Twin, Part 1. http://www.youtube.com/watch?v=wtZgxsAkA3s Last accessed: May 19, 2009.
The website of Lydia Fairchild, including some files of various magazine articles about her. http://www.geocities.com/mylifewithchimera/4.html Last accessed: May 19, 2009.
2 According to Brooker, a chimera is an organism composed of cells that are embryonically derived from two individuals. See: Brooker, R.J. 2009. Genetics: Analysis and Principles, 3rd edition, McGraw Hill Higher Education.
3 See: Dewald, G., M.W. Haymond, J.L. Spurbeck, and S.B. Moore. 1980. Origin of chi46,XX/46,XY chimerism in a human true hermaphrodite. Science 207(4428):321–323.
4 See: Yu, N., et al. 2002. Disputed maternity leading to identification of tetragametic chimerism. New England Journal of Medicine 346(20):1545–1552.
5 See: Boklage, C.E. 2006. Embryogenesis of chimeras, twins and anterior midline asymmetries. Human Reproduction 21(3):579–591.
6 See: Dewald, G., M.W. Haymond, J.L. Spurbeck, and S.B. Moore. 1980. Origin of chi46,XX/46,XY chimerism in a human true hermaphrodite. Science 207(4428):321–323.
7 See: Yu, N., et al. 2002. Disputed maternity leading to identification of tetragametic chimerism. New England Journal of Medicine 346(20):1545–1552.
8 See: Hutchison, J. 2007. Giving Birth to Someone Else’s Children? A Case of Disputed Maternity at http://www.sciencecases.org/chimera/chimera.asp; Teaching Notes for “Giving Birth to Someone Else’s Children?” at http://www.sciencecases.org/chimera/chimera_notes.asp, National Center for Case Study Teaching in Science.
Acknowledgements: This case was published with support from the National Science Foundation under CCLI Award #0341279. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Date Posted: October 13, 2009.
Originally published at http://www.sciencecases.org/disputed_maternity/notes.asp
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