A genetic disease is any disease that is caused by an abnormality in an individual’s genome. The abnormality can range from minor to major – from a discrete mutation in a single base in the DNA of a single gene to a gross chromosome abnormality involving the addition or subtraction of an entire chromosome or set of chromosomes.
Some genetic disorders are inherited from the parents, while other genetic diseases are caused by acquired changes or mutations in a preexisting gene or group of genes. Mutations occur either randomly or due to some environmental exposure.
Genome: All of the genetic information, the entire genetic complement, all of the hereditary material possessed by an organism.
Humans and many other higher animals actually have two genomes, which together make up the total genome:
- A chromosomal genome – inside the nucleus of the cell in the familiar form of chromosomes; and
- A mitochondrial genome – outside the nucleus in the cytoplasm of the cell, usually in the form of one round chromosome (the mitochondrial chromosome).