Traits
Traits are characteristics each person has that make up everything about him. These can include physical characteristics such as appearance, as well as psychological characteristics, like a tendency to be creative or optimistic. Some traits, including many aspects of psychology, are believed to be created or influenced by the world around a person, her environment. Many traits, however, are inherited from parents through DNA. Common traits known to be inherited include eye color, hair color and texture, the presence of attached or detached earlobes and a wide variety of diseases, including sickle cell anemia, hemophilia and cystic fibrosis. Other traits have a mixture of inheritance and environmental influences that affect the final outcome in the child, including many diseases such as Alzheimer's disease and bipolar disorder.
DNA and Chromosomes
DNA is the fundamental component that carries all genetic information in every cell of the human body. Each individual inherits half of his DNA from each parent. This DNA is coiled into chromosomes, 23 from each parent, to provide a total of 46 chromosomes' worth of genetic information. The mechanism by which this occurs is that the parent's cells divide during a process called meiosis to create eggs or sperm with 23 chromosomes inside. When egg and sperm join during fertilization, the 23 chromosomes from each parent pair up to make the 46 chromosomes of the offspring.
Gene Expression
As the offspring develops, the DNA on the chromosomes directs its cells to express specific traits. Sometimes both inherited chromosomes give the same instructions, which causes that trait to be expressed. For example, if a child inherits the gene for an attached earlobe from both parents, the attached earlobe trait will be expressed and the child will also have an attached earlobe.
In other cases, the two inherited chromosomes give different instructions. In this case, if one is dominant over the other, the child will exhibit that trait. For example, when one parent's chromosome indicates an attached earlobe and the other indicates a detached earlobe, the dominant detached earlobe trait will win out and the child will have a detached earlobe.
Some traits are more complex and will create a blend of the two traits or will involve multiple genes, sometimes on different chromosomes, to influence the final outcome in the offspring. Other inherited traits will interact with environmental effects to show up in the child only if the environmental conditions are right.
