As all complex human traits are influenced by lots of different genes (pieces of DNA encoded information) – see Mendel and More – each gene tends to have a very tiny influence on a trait. Even though some genes have been found to be associated with human traits, at best these can explain only about 1% of variation in that trait. It is much more common for genes to have even smaller influences.
Twins studies are very useful for looking at the relative influences of genes and environments in what makes each of us different and unique. By looking at certain traits in twins’, scientists have found that genetic influences account for between 40% and 80% of trait differences seen in any given population.
Now that we are able to look directly at the genome, scientists are starting to make use of an exciting new technique called Genome-wide Polygenic Scoring (GPS). To do this, they look for the thousands of genes most associated with a particular trait and then sum these together to give a GPS. This GPS can then be used to make predictions about other traits. One such GPS (EduYears) has recently been used to predict school achievement. Students with the highest EduYears score typically achieved one whole grade higher than students with the lowest EduYears score. These predictions will never be perfect as the environment is so important, but they do help us understand the relationship between our genomes and who we are. As our DNA does not change, these GPS scores can theoretically be tested as soon as we are born.