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.

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.

Autosome
A chromosome not involved in sex determination.

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

Mutation
Any heritable change in DNA sequence.

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

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.

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

Cancer
Diseases in which abnormal cells divide and grow unchecked.