Birth Defect Terms and Definitions

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.

Birth defect
Any harmful trait, physical or biochemical, present at birth, whether a result of a genetic mutation or some other nongenetic factor.

Centromere
A specialized chromosome region to which spindle fibers attach during cell division.

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

Phenotype
The physical characteristics of an organism or the presence of a disease that may or may not be genetic.

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

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.

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

Gene
The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product

Amino acid
Any of a class of 20 molecules that are combined to form proteins in living things.