You Are Not the Mother of Your Children by Stephen R. Cronin

Part III – Alternate Epilogue: But How Does It Happen?

After carefully analyzing DNA sampled from different parts of Lillian’s body, Dr. Vijayvergia and his graduate students found that Lillian was indeed chimeric. They were not been able to sample her ovarian tissue, since that would have required an invasive surgery. However, hair follicles from a patch of skin on her left leg reliably yielded DNA that differed from her cheek cell DNA, and matched the DNA of her children. Lillian had retained custody of her children, and in a twist worthy of the tabloids, the court case had brought her and her boyfriend back together. Indeed, the whole story was reported in the National Enquirer and several other magazines. News shows interviewed Lillian, and Dr. Vijayvergia was interviewed for a documentary on the Discovery Health cable channel.

But for Dr. Vijayvergia, the biological questions remained: How did it happen? Could the occurrence of chimeric individuals be explained by some exceptional event in the process of gamete formation or fertilization? What hypotheses could explain the formation of chimeras?

Questions

1. Using your knowledge of the normal process of gametogenesis and fertilization, formulate several alternative hypotheses as to how a chimeric individual could form.

   After formulating your hypotheses, read the article by Dewald, Haymond, Spurbeck, and Moore: “Origin of chi46,XX/46,XY Chimersim in a Human True Hermaphrodite,” Science 207:321–323 1980.

   Answer the following questions based on the article. To answer the questions, you will probably need to look up some of the terms in a medical dictionary.

2. In the first paragraph, what ways do the authors suggest whole body chimeras could form?

3. Use a textbook or other reliable source of information to find out what is currently known about polar bodies. What are polar bodies? When do they form? According to current understanding, what happens to polar bodies?

4. The authors note that almost all chimeras known at the time of the study had sexual abnormalities, such as true hermaphroditism (presence of both make and female reproductive organs). What reason do they hypothesize for the scarcity of known cases of chimerism without sexual abnormalities?

5. According to the fourth paragraph, what was done surgically to the child? What consequences would this have for the child’s future development?

6. The authors conclude that the child formed from the fusion of a fertilized embryo, fused with the product of a separately fertilized polar body from the second meiotic division.

   1. What evidence do they have that supports this interpretation?

   2. What evidence do they have that argues against the other hypotheses listed in the first paragraph?

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