When humans’ genetic information (known as the genome) was mapped 15 years ago, it promised to change the world. Optimists anticipated an era in which all genetic diseases would be eradicated. Pessimists feared widespread genetic discrimination. Neither of these hopes and fears have been realised.
The reason for this is simple: our genome is complex. Being able to locate specific differences in the genome is only a very small part of understanding how these genetic variants actually work to produce the traits we see. Unfortunately, few people understand just how complex genetics really is. And as more and more products and services start to use genetic data, there’s a danger that this lack of understanding could lead people to make some very bad decisions.
At school we are taught that there is a dominant gene for brown eyes and a recessive one for blue. In reality, there are almost no human traits that are passed from generation to generation in such a straightforward way. Most traits, eye colour included, develop under the influence of several genes, each with its own small effect.
What’s more, each gene contributes to many different traits, a concept called pleiotropy. For example, genetic variants associated with autism have also been linked with schizophrenia. When a gene relates to one trait in a positive way (producing a healthy heart, say) but another in a negative way (perhaps increasing the risk of macular degeneration in the eye), it is known as antagonistic pleiotropy.
As computing power has increased, scientists have been able to link many individual molecular differences in DNA with specific human characteristics, including behavioural traits such as educational attainment and psychopathy. Each of these genetic variants only explains a tiny amount of variation in a population. But when all these variants are summed together (giving what’s known as a characteristic’s polygenic score) they begin to explain more and more of the differences we see in the people around us. And with a lack of genetic knowledge, that’s where things start to be misunderstood.