Birth Defect Terms and Definitions

Embryonic stem (ES) cells
An embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells.

Deletion.
A loss of part of the DNA from a chromosome; can lead to a disease or abnormality.

Single-gene disorder
Hereditary disorder caused by a mutant allele of a single gene.

Bacterial artificial chromosome (BAC)
A vector used to clone DNA fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli cells.

Autosome
A chromosome not involved in sex determination.

Mutation
Any heritable change in DNA sequence.

Hybrid
The offspring of genetically different parents.

Genetic illness
Sickness, physical disability, or other disorder resulting from the inheritance of one or more deleterious alleles.

Junk DNA
Stretches of DNA that do not code for genes; most of the genome consists of so-called junk DNA which may have regulatory and other functions.

Mitosis
The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell.