For over a hundred years, scientists investigating human behavior or medicine have assumed that identical twins carry identical genes. Now, Shiva Singh, a researcher from the University of Western Ontario studying molecular genetics, believes that twins aren’t actually duplicates.
Singh’s research dealt with schizophrenia and heredity. Schizophrenia is more likely if one’s parents or siblings have the disease. Singh theorized that an identical twin whose twin sibling had schizophrenia would have a 100 percent chance of developing it, since identical, or monozygotic, twins are created from one divided fertilized egg. But Singh has discovered that the risk of both twins developing schizophrenia is 50 percent, not 100 percent, as hypothesized.
Singh studied the DNA sequences of twins along with the DNA of their parents and considered the genes’ differences. According to Singh, the genes in human cells change, either decrease or increase, as the cells age and reproduce. Genes and the ways people manifest them vary constantly. Singh said, “The implication would be that there is nobody with the [identical] human genome sequence.” Singh also believes that twins become more different from each other as they age.
The discovery carries implications for scientists studying medical or psychological matters that have genetic underpinnings.