随身英语 Is DNA testing accurate? DNA 测试准吗？

陈小将

你和你的兄弟姐妹有相同的父母，相同的祖先，但是怎么可能会有不同的祖先基因？本文讨论同家族成员为什么有不同的 DNA 和造成基因测试不准确的因素。
词汇：ancestry 祖先
Have you ever wondered why your brother or sister doesn’t look exactly like you despite having the same family tree? If you think that’s odd, even stranger is the idea that you and your sibling may have very different ancestry genes. You have the same parents, and therefore the exact same ancestors, but somehow your DNA tests come back with very different results. How is this even possible?
Children inherit half of their DNA from each parent, via the sperm from the father and the egg from the mother. Our bodies contain 46 chromosomes, or 23 pairs. However, each reproductive cell has only 23 individual chromosomes. When the bodies of our forbearers created their sex cells, the cells engaged in genetic reshuffling, meaning each of the 23 chromosomes is a unique combination of an original pair. This process is also called genetic recombination.  
This is why Dr. Prosanta Chakrabarty, a scientist who studies fish to help explain the evolution of human beings and our planet, says that your sister could be 10% more 'French' than you, despite having the same primogenitors. And the further you go back in your lineage, the more confusing it can be.
You inherit 25% of each grandparent's DNA. However, this process of recombination means that inevitably some of their genetic make-up will be lost along the way. This could mean that the genes you inherited from your grandparent, could be completely different to those your cousin received.  
Those studying genealogy should also be aware that modern DNA testing might not give you an accurate idea of your ancestry as it is tested against a current, but incomplete database. Many of the genetic samples come from North America and Western Europe. The genes passed down from your ancestors is sampled and matched with people who originated from a certain area. However, without enough samples from the Middle East or Africa, the results may be inaccurate.
Dr. Prosanta Chakrabarty says that only 1% of our genetic make-up is unique to us, and that it is an incomplete mash-up of our ancestors'. So, the next time someone says you look a bit like you're from a certain country, you may well be. But it might not show up in your tests.