Heredity

Parents pass on certain traits to their children. These traits include eye color, hair color, height, and other physical characteristics. The coding for these traits lies inside all human cells, specifically within molecules called deoxyribonucleic acid (DNA). DNA is basically the biological blueprint for each unique person.

Since the discovery of DNA, the science of genetics has focused on the study of DNA and the ways in which physical traits are transmitted from generation to generation. Within genetics, a special branch of DNA science—called quantitative, or biometrical, genetics—has emerged. This branch studies the heritability of such traits as intelligence, behavior, and personality, and focuses on the effects of so-called polygenes in the creation of certain phenotypes. The term polygene refers to the interaction of several genes.

The outward expression, or phenotype, of this overall biological blueprint includes certain variable characteristics of behavior or personality. Quantitative geneticists, therefore, study the effects of groups of genes on the development of personality and other abstract variables. While one specific gene is sometimes found to be responsible for one disease, this one-to-one association is atypical. Likewise, researchers are only rarely able to pinpoint the genesis of a behavior to one specific gene.

In addition, genetics is usually not the sole predictor of behavior or other cognitive traits. Often environmental factors play an important role. Research studies have repeatedly demonstrated that such characteristics are a result of heredity and life experiences, although one may be more influential than another depending on the trait studied. Memory, age of language acquisition, and reading disabilities are some of the intellectual characteristics often associated with heredity. Among emotional characteristics, heredity has been linked with shyness, extroversion, neuroses, anxiety, and alcohol dependence. This does not mean that a parent who is shy and has a bad memory will only have children who are timid and cannot remember names. Rather, this indicates that children of such a parent are more likely to exhibit tendencies toward shyness or a poor memory ability. Many children of alcoholics, for instance, do not become alcoholics themselves. Instead, a child who is genetically vulnerable to acquiring alcoholism, may never drink because he or she has witnessed first-hand the effects of alcoholism on the family. In other words, the genetic tendency may be present, but life experiences help to shape the ultimate outcome for that individual.

Many scientists are studying epigenetics, which focuses on the interaction between heredity and environmental factors, or what is commonly described as “nature vs. nuture.” Epigenetics investigates the role of environmental factors in turning genes on or off. When a gene is turned on, it is “expressed,” which means that it becomes involved in the process to create proteins and other molecules that allow the generelated characteristic to appear. Research has found many such links between environmental factors and gene expression.