Recurrence Risk

Chromosomal aberrations may be inherited from a parent, and because of this many families seek genetic counseling in order to determine if a genetic disorder will recur in another member of the same generation or in generations that will follow. The family needs to know the genetic risk, also known as the recurrence risk, and any means by which transmission may be prevented. A recurrence risk will be calculated based on the accuracy of the diagnosis, the pedigree of the family, and the known genetic mechanisms of the disorder in question. see also Birth Defects; Chromosome Banding; Crossing Over; Down Syndrome; Meiosis; Mutation; Nondisjunction; Prenatal Diagnosis.

Jacqueline Bebout Rimmler


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Chromosomal Banding

A chromosome banding pattern is comprised of alternating light and dark stripes, or bands, that appear along its length after being stained with a dye. A unique banding pattern is used to identify each chromosome and to diagnose chromosomal aberrations, including chromosome breakage, loss, duplication or inverted segments. In the 1950s, chromosomes from the cell's nucleus were identified with a uniform (unbanded) stain that allowed for the observation of the overall length and primary constriction (centromere) of each chromosome, as well as a secondary constriction in chromosomes 1, 9, 16 and the acrocentrics (chromosomes whose centromeres are near the tips). The staining techniques used to make the bands visible were developed in the late 1960s and early 1970s.

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