Part II – A Strange Child
“Damian, I think I’ve found some research papers that might explain the case you told me about. My hypothesis is your client, the mother, is a chimera, a person with two genetically distinct sets of cells. Several children have been born who are genetic chimeras.”
Dr. Rajesh Vijayvergia was a professor of biology and certainly talked like one.
“Here’s an example from one of the papers. In 1980, a child was born with ambiguous genitalia and they found the child was a true hermaphrodite, had both testicular and ovarian tissue, male and female at the same time. They found that the male parts of the child had an X and a Y chromosome, and the female parts of the child had two X’s. Importantly, a comparison of the autosomal DNA (the non-sex chromosomes) showed that the DNA from the male cells was different from the female cells. So the child had two complete sets of DNA in different cells: Some cells with one set of chromosomes and genetically male, and the other cells with the other set of chromosomes and genetically female.”
“Rajesh, can you translate for me?” asked Damian.
“Yes, yes. Genetically the child looked like a fusion of two different genetic individuals. Like fraternal twins that grew together to form one person, instead of growing separately.”
“So, how does this relate to my case?”
“I know what you are thinking. Your client has two children, not one, and both are perfectly normal. My hypothesis is your client, the mother, is a chimera. She is her own fraternal twin.”
“Rajesh, as far as I know my client’s sex isn’t ambiguous.”
“I know, I know. The child I was telling you about attracted attention because he/she was half male and half female. A person with two sets of cells that were both genetically female might not attract any attention at all. She would grow and develop like any other woman. If you didn’t look at her DNA, you would never know. When they tested DNA from her cheek cells they found one set of DNA, but I think other parts of her are composed of a different cell line, one with DNA distinct from that of her cheek cells. If this cell line contributed the DNA to her oocytes, then her children would have inherited that DNA, not the DNA seen in her cheek cells. That could explain why the mother’s DNA test doesn’t match with her children’s.”
“Is there any way we can find out if you’re right?
“Yes, I think we can try.”
Questions
What is a chimera?
What are fraternal twins, and how do they normally occur? How much of their DNA would you expect fraternal twins to share?
Why does Dr. Vijayvergia think the mother (Lillian) can be a chimera and not appear abnormal?
How could Dr. Vijayvergia’s hypothesis be tested? What could you do to find out if Lillian was a chimera?
Originally published at http://www.sciencecases.org/disputed_maternity/case2.asp
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