gene

the fundamental unit of genetic material found at a specific location on a CHROMOSOME . It is chemically complex and responsible for the transmission of information between older and younger generations. Each gene contributes to a particular trait or characteristic. There are more than 100,000 genes in humans, and gene size varies with the characteristics, e.g. the gene that codes for the hormone INSULIN is 1,700 base pair long. There are several types of gene, depending on their function, and in addition genes are said to be dominant or recessive. A dominant characteristic is one that occurs whenever the gene is present while the effect of a recessive gene (e.g. a disease) requires that the gene be on both members of the chromosome pair, i.e. it must be homozygous. See also SEX-LINKED DISORDERS .