trisomy

(noun)

The presence of three copies, instead of the normal two, of a particular chromosome of in an organism.

Related Terms

Examples of trisomy in the following topics:

  • Down Syndrome

    • Down syndrome is a developmental disorder caused by trisomy 21, or the presence of an extra 21 chromosome.
    • Trisomy 21 is caused by a meiotic nondisjunction event.
    • Trisomy 21 is usually caused by nondisjunction in the gametes prior to conception, and all cells in the body are affected.
    • However, when some of the cells in the body are normal and other cells have trisomy 21, it is called mosaic Down syndrome.
    • There is considerable variability in the fraction of trisomy 21, both as a whole and among tissues.

  • Prenatal Diagnostic Tests

    • Blood tests for select trisomies based on detecting fetal DNA present in maternal blood are available.
    • The results of the blood tests are then combined with the NT ultrasound measurements, maternal age, and gestational age of the fetus to yield a risk score for Down syndrome, trisomy 18, and trisomy 13.

  • Alzheimer's Disease

    • Support for this postulate comes from the location of the gene for the amyloid beta precursor protein (APP) on chromosome 21, together with the fact that people with trisomy 21 (Down syndrome) who have an extra gene copy almost universally exhibit AD by 40 years of age.