<Li> In plants: Seven genetically distinct yarrow plants were collected and three cuttings taken from each plant . One cutting of each genotype was planted at low, medium, and high elevations, respectively . When the plants matured, no one genotype grew best at all altitudes, and at each altitude the seven genotypes fared differently . For example, one genotype grew the tallest at the medium elevation but attained only middling height at the other two elevations . The best growers at low and high elevation grew poorly at medium elevation . The medium altitude produced the worst overall results, but still yielded one tall and two medium - tall samples . Altitude had an effect on each genotype, but not to the same degree nor in the same way . </Li> <Li> Phenylketonuria (PKU) is a human genetic condition caused by mutations to a gene coding for a particular liver enzyme . In the absence of this enzyme, an amino acid known as phenylalanine does not get converted into the next amino acid in a biochemical pathway, and therefore too much phenylalanine passes into the blood and other tissues . This disturbs brain development leading to mental retardation and other problems . PKU affects approximately 1 out of every 15,000 infants in the U.S. However, most affected infants do not grow up impaired because of a standard screening program used in the U.S. and other industrialized societies . Newborns found to have high levels of phenylalanine in their blood can be put on a special, phenylalanine - free diet . If they are put on this diet right away and stay on it, these children avoid the severe effects of PKU . This example shows that a change in environment (lowering Phenylalanine consumption) can affect the phenotype of a particular trait, demonstrating a gene - environment interaction . </Li> <Li> A single nucleotide polymorphism rs1800566 in NAD (P) H Quinone Dehydrogenase 1 (NQO1) alters the risk of asthma and general lung injury upon interaction with NOx pollutants, in individuals with this mutation . </Li> <Li> A functional polymorphism in the monoamine oxidase A (MAOA) gene promoter can moderate the association between early life trauma and increased risk for violence and antisocial behavior . Low MAOA activity is a significant risk factor for aggressive and antisocial behavior in adults who report victimization as children . Persons who were abused as children but have a genotype conferring high levels of MAOA expression are less likely to develop symptoms of antisocial behavior . These findings must be interpreted with caution, however, because gene association studies on complex traits are notorious for being very difficult to confirm . </Li>

How genes and environment determine an organism's characteristics