Birth Defect Terms and Definitions

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

Codominance
Situation in which two different alleles for a genetic trait are both expressed.

Syndrome
The group or recognizable pattern of symptoms or abnormalities that indicate a particular trait or disease.

Hybrid
The offspring of genetically different parents.

Haploid
A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals and in the egg and pollen cells of plants

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

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.

Fraternal twin
Siblings born at the same time as the result of fertilization of two ova by two sperm. They share the same genetic relationship to each other as any other siblings.

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

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