Genetics and Health

Human Genetic Chimeras

by Hsien Hsien Lei, PhD on August 25th, 2005

Man, it’s a tough blogging day when I start talking about recursive splicing of mRNA and the dissipation of energy from UV radiation along the DNA backbone.

Here’s a story from the entertainment section of the Philadelphia Inquirer about a mother who needed a donor kidney. The most likely matches were her three sons who, by the laws of Mendelian genetics, should share 50 percent of her genes. When they were all tested, though, none of her sons were a match. A hospital mix-up was ruled out because the boys’ DNA matched their father’s. Subsequent tests discovered that mom was a chimera.

Chimeras get their start when two or more eggs are released and fertilized by different sperm. That usually results in fraternal twins. Unlike identical twins, fraternal twins are no more genetically alike than ordinary siblings.

In a few cases, though, fraternal twins merge while in utero, becoming one single individual with a mosaic of different types of cells carrying distinct genetic codes.

The mother’s blood cells carried DNA from one twin, her ovaries and eggs carried DNA from another.

You can read the full story and more about human chimeras, which was originally published in New Scientist, November 15, 2003. It’s a cliffhanger - we don’t know if the mother ever got the kidney transplant she needed.

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POSTED IN: Genetics of Disease