Genetics Northern California



Ductal carcinoma in situ. Cancer limited to the ducts of the breast. It may or may not become invasive.

De novo mutationA genetic mutation occurring for the first time; not found in a previous generation.
DeformationA type of structural defect characterized by the abnormal form or position of a body part caused by mechanical force.

The loss of a sequence of DNA from a chromosome. The deleted DNA may be of any length from a single base to a large part of a chromosome.

Developmental Delay(s)

Cognitive and/or motor delays in development. Progress/prognosis is dependent on the severity of delays and the underlying condition, but in most instances, children with delayed development never fully "catch up." Definition from Website: A slowing of the usual process of development particularly of cognitive skills.


The determination of the nature of a disease or condition.


Having a full set of genetic material consisting of paired chromosomes with one chromosome from each parent. In humans, the diploid chromosome number is 46.


The morphologic defect of an organ or larger region of the body resulting from the disturbance or destruction of an originally normal developmental process.


The product of fertilization of two separate eggs by two separate sperm; nonidentical twin pair. Compare to monozygotic.


Deoxyribonucleic acid; the molecule that encodes the genes responsible for the structure and function of living organisms and allows the transmission of genetic information from generation to generation.

DNA Methylation

Addition of a methyl group to a cytosine base in the DNA molecule. This process plays a role in gene expression that is not completely understood.


A characteristic of gene expression in which only one copy of a gene is needed in order for there to be manifestations of its presence.

Down Syndrome

A condition involving mental retardation due to the presence of an extra chromosome 21. Also called trisomy 21.


The presence of an extra copy of chromosomal material.


Reflecting abnormality in morphological development; abnormality in the development of structure or form.


Abnormality of development of particular tissue types; alteration in size, shape, or organization of cells into tissue.