2025年12月英语四级（第3套 · 含听力）仔细阅读 Passage 2

Genetic tests are being used for a growing number of purposes, from diagnosing diseases to finding out about our ancestors. But how accurate are these tests? And what does accuracy even mean in this context? There are important things to understand about genetic testing accuracy.
The accuracy of a genetic test depends on the specific question being asked and how complex the genetics behind a trait are. For relatively simple genetic conditions where a single gene is responsible, tests tend to be quite reliable. For example, tests for conditions like cystic fibrosis (囊性纤维化) or sickle cell disease (镰状细胞病) are generally very accurate because we understand the genetic basis of these diseases well.
However, for most common diseases, the picture is more complicated. Conditions like heart disease, diabetes, and most cancers are influenced by hundreds of genes, each contributing a small amount of risk. They are also affected by environmental factors and lifestyle choices. For these multi-factorial conditions, genetic health tests can only identify a fraction of the potential disease risk on their own.
What makes genetic tests for multi-factorial traits particularly tricky to interpret is the interaction between genes. Even if we know that hundreds of genes are involved in a trait, predicting how those genes will interact with each other is extremely difficult. The combined effect of multiple genes is not simply the sum of their individual effects.
Some companies also offer DNA tests that claim to predict personality traits, athletic ability, or even help you find a romantic partner. At present, using DNA to predict such complex traits does not have a solid scientific basis. The genetics behind personality and talents involve thousands of genes and complex environmental interactions, making any predictions essentially meaningless with current technology.