Glossary of Terms

Genetic Diseases

Birth defect:
A structural, functional, or metabolic abnormality present at birth that results in physical or mental disability.

Carrier:
An individual who possesses and can transmit the gene for a given disease but does not exhibit the disease. Although carriers are not affected by the disease, two carriers can produce a child who has the disease.

Cell:
The basic unit of any living organism. It is a small, watery, compartment filled with chemicals and a complete copy of the organism's genome.

Chromosome:
One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.

Congenital:
Any trait or condition that exists from birth.

DNA:
Deoxyribonucleic acid; the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

Dominant:
A single gene whose characteristics are expressed in an individual in whom that gene is present.

Gene:
The basic unit of heredity passed from parent to child. Genes determine our various characteristics such as hair color and texture, eye and skin color, height, etc.

Genetic counseling:
A short-term educational counseling process for individuals and families who have a genetic disease or who are at risk for such a disease. Genetic counseling provides patients with information about their condition.

Genetic screening:
Testing a population group to identify a subset of individuals at high risk for having or transmitting a specific genetic disorder.

Genetic testing:
Analysis of DNA, chromosomes, or gene products that provide specific information about inherited variations in genes or chromosomes of an individual.

Geneticist:
A medically qualified professional who specializes in the study of heredity and its variation.

Genetics:
The study of hereditary and the patterns of genetic inheritance among organisms.

Genome:
All of the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.

Genomics:
The study of the genome and its actions. Genomics involves the analysis of the full DNA sequence of the organism. Genomics addresses the working of all genes and their inter-relationships in order to identify their combined influence on the growth and development of the organism.

Human Genome Project:
An international research project to map each human gene and to completely sequence human DNA.

Inherited:
Transmitted through genes from parents to offspring.

Mendelian inheritance:
Manner in which genes and traits are passed from parents to children. Examples of Mendelian inheritance include autosomal dominant, autosomal recessive, and sex-linked genes.

Mutation:
A permanent structural alteration in DNA. In most cases, DNA changes either have no effect or cause harm, but occasionally a mutation can improve an organism's chance of surviving and passing the beneficial change on to its descendants.

Recessive:
A genetic disorder that appears only in patients who have received two copies of a mutant gene, one from each parent.