A

GENOTYPE

The term "genotype" refers to the specific genetic makeup of an individual and is often used with reference to allelic or mutant differences between individuals at one or more genes. The genotype of an individual is the genetic information within an individual's specific DNA sequence that sets the limits upon which nongenetic parameters like environment modulate normal and abnormal phenotypes. Geno-types at specific genes known to cause birth defects are used as diagnostics in genetic counseling to identify parents carrying specific disease genes and in prenatal genetic testing for offspring that will have birth defects. For example, a description of a mutation within the gene that causes cystic fibrosis is a geno-type, while manifestation of the disease is the pheno-type. The results of the Human Genome Project are being used to identify DNA sequences that cause birth defects. The genotypes associated with birth defects are then available for development of more accurate diagnostic tests.