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.

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.

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

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

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

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.

Pedigree
A family tree diagram that shows how a particular genetic trait or disease has been inherited.

Autosome
A chromosome not involved in sex determination.

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

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