Birth Defect Terms and Definitions

Identical twin
Twins produced by the division of a single zygote; both have identical genotypes.

Risk communication
In genetics, a process in which a genetic counselor or other medical professional interprets genetic test results and advises patients of the consequences for them and their offspring.

Cancer
Diseases in which abnormal cells divide and grow unchecked.

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

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

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

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

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

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

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