Gene is unit of heredity in all living organisms. A gene is part of a DNA molecule within the nucleus of all cells. Each gene codes for a particular protein. Thus a gene is a unit of the inheritable characteristics of the organism. Humans have tens of thousands of different genes; these determine the phenotype of the individual.
According to new study our level of happiness throughout life is strongly influenced by the genes with which we were born.
An Edinburgh University study of identical and non-identical twins suggests genes may control half the personality traits keeping us happy. The other half is linked to lifestyle, career and relationships.
So if you are not happy, just blame to your genes ;). On a related note positive thinking may improve overall life.