Study: Identical Twins Do Not Always Have the Exact Same Genes


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A new study has found that identical twins have more genetic differences than originally thought. For decades, identical twins were believed to share the same genes because they develop from a single egg cell that splits into two. Experts had presumed that any physical, behavioral, or health differences between identical twins could only be caused by environmental factors, such as their lifestyles or the food that they eat. Because of this, scientists have long used identical twins in nature versus nurture studies, which investigate whether certain human behaviors are caused by genetics or the environment. However, new research shows that this presumption is not accurate. For four years, scientists in Iceland studied the complete genetic makeup of 387 pairs of identical twins, as well as their parents, children, and spouses, to look for any mutations. Genetic mutations occur when changes happen in a person’s DNA sequence. They can affect a person's physical traits or health. Mutations are mostly harmless, but some are more serious and can increase susceptibility to certain illnesses like cancer. The scientists found that, on average, identical twins have only 5.2 genetic differences between them, but they also discovered that around 15% of identical twins have more than that. These differences constitute only a small portion of each twin’s genetic makeup, but they could create great differences in the twins' health and appearances. The study is being hailed as a significant contribution to medical research. Geneticist Jan Dumanski said that its findings show that scientists should be careful when using twins in nature versus nurture experiments.

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