For some genetic disoders, genetic counseling and prenatal diagnosis may be advised. The terms anomaly, abnormality, disorder, defect, disease, and syndrome are not used consistently and do not have precise definitions. Each chromosome is comprised of 2 extremely long DNA molecules in combination with chromosomal proteins . Genes are defined by intervals along one of the DNA molecules. The location of the gene is called the locus.
Most genes carry information which is necessary to synthesize a protein .
Alleles are different variants of a particular gene. This protein may be a structural constituent of a given tissue. It may be an enzyme which catalyzes a chemical reaction, or it may be a hormone. There are also many other potential functions for proteins. If a gene is abnormal, it may code for an abnormal protein or for an insufficient amount of a normal protein.