HOW GENES WORK: Everyone has a set of chromosomes, each containing two halves, one from each parent, and each containing a complete set of genes, so that each chromosome has two copies of every gene. The "dominant" gene is the one that is expressed, such as for brown eyes. A "recessive" gene produces a particular trait -- for instance, for blue eyes -- only if its effects are not over-ridden by those of a dominant gene. Genes are normally transmitted unchanged from one generation to the next, but sometimes a mutation occurs: the structure of the gene is changed. Genetic engineers study these mutations in hopes that it may one day be possible to correct errors in genetic coding that are responsible for specific diseases or disorders.
WHAT IS DNA? DNA is the blueprint that encodes all the data for building a human body, along with instructions on how it should operate. Every cell in a person's body contains a copy of this DNA. DNA typing is based on an unusual feature found in the human genome. There are multiple copies of certain short sequences, 3 to 30 base pairs long, that are repeated one after another as many as 100 times. These groups of repeat sequences are widely scattered through the genome. Everyone has these repeat units, but the number varies from person to person. Only identical twins will have the same numbers and patterns of these sequences. These genetic data aren't instructions to make anything; scientists think they might exist to get mixed up in the regular genes and provide some variety for evolution.
The Biophysical Society contributed to the information contained in the TV portion of this report.