Genotype or phenotype
![Genotypes are the genetic make-up of an individual.
Phenotypes are the physical traits and characteristics of an individual and are influenced by their genotype and the environment.](https://www.ebi.ac.uk/training/online/courses/human-genetic-variation-introduction/wp-content/uploads/sites/76/2020/06/fig3-1-1024x399.png)
Genetic differences or variation between individuals leads to differences in an individual’s phenotype, trait or risk of developing a disease. An individual’s phenotype is influenced both by their genotype and their environment (Figure 3).
A mendelian trait is one that is controlled by a single locus, for example a single base-pair substitution. In most cases, associations between genetic variants and phenotypes/traits are not this simple. These are called complex phenotypes and may be influenced by multiple variants in the genome along with environmental factors.