Urban Lab - Stanford University School of Medicine. The impact of chimerism in DNA-based forensic sex determination analysis. DNA Double Take. But scientists are discovering that — to a surprising degree — we contain genetic multitudes. Not long ago, researchers had thought it was rare for the cells in a single healthy person to differ genetically in a significant way. But scientists are finding that it’s quite common for an individual to have multiple genomes.
Some people, for example, have groups of cells with mutations that are not found in the rest of the body. Some have genomes that came from other people. “There have been whispers in the matrix about this for years, even decades, but only in a very hypothetical sense,” said Alexander Urban, a geneticist at Stanford University. Even three years ago, suggesting that there was widespread genetic variation in a single body would have been met with skepticism, he said. But a series of recent papers by Dr. Dr. Science’s changing view is also raising questions about how forensic scientists should use DNA evidence to identify people. Human Blueprint Everywhere You Look Dr. Dr. Human Chimeras. Imagine a welfare mother denied custody of her children because her DNA points to her not being their mom. Or another mother who cannot get a kidney transplant from her son because they do not share enough DNA. Strange stories like these are becoming increasingly common in this new age of DNA testing.
In both cases, the moms really were the moms. They each are just made up of two different sets of cells with different DNA—they are chimeras. How Chimeras Happen In Greek mythology, a chimera was a beast made of a lion, a goat and a dragon. A human chimera is made up of two sets of cells with DNA as different as any two siblings’ DNA.
This can happen because early on, embryos are made up of embryonic stem (ES) cells. Combining two sets of ES cells with different DNA has no consequences for the new chimera. Getting the Wrong DNA Results A DNA test is usually done by taking some blood or cheek cells and looking at the DNA. The children looked like nephews or nieces with one set of cells. Mosaicism and Chimerism. Mosaics and chimeras are animals that have more than one genetically-distinct population of cells. The distinction between these two forms is quite clearly defined, although at times ignored or misused. In mosaics, the genetically different cell types all arise from a single zygote, whereas chimeras originate from more than one zygote.
Mosaics are not uncommon; in fact, roughly half of the mammals on earth are a type of mosaic. A chimera, on the other hand, is not something you're likely to come across unless you are an experimental embryologist or raise cattle. Cytogenetic Mosaics The term mosaic is usually applied to an animal that has more than one cytogenetically-distinct population of cells. What is the clinical significance of mosaicism? X chromosome Mosaicism Early in embryogenesis in mammals, all but one X chromosome are functionally inactivated through a process called X chromosome inactivation. The gene encoding orange coat color is X-linked (that is, on the X chromosome).