trisomy

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.

• Disorders in Chromosome Number

  • The gain of one chromosome is called trisomy (2n+1).They are caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis.
  • Klinefelter syndrome is a trisomy genetic disorder in males caused by the presence of one or more X chromosomes.
  • The effects of trisomy are similar to those of monosomy.
  • Down syndrome is the only autosomal trisomy in humans that has a substantial number of survivors one year after birth.
  • Trisomy in chromosome 21 is the cause of Down syndrome; it affects 1 infant in every 800 live births.

• Prenatal Diagnostic Tests

  • Blood tests for select trisomies based on detecting fetal DNA present in maternal blood have become 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.

• X-Inactivation

  • Humans display dramatic deleterious effects with autosomal trisomies and monosomies.

• Identification of Chromosomes and Karyotypes

  • This was discovered after the naming of Down syndrome as trisomy 21, reflecting how this disease results from possessing one extra chromosome 21 (three total).

• 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.Also APOE4, the major genetic risk factor for AD, leads to excess amyloid buildup in the brain.

• Intellectual Disabilities

  • Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of a full or partial third copy of chromosome 21.

• Gene Duplications and Divergence

  • For example, trisomy 21 in humans leads to Down syndrome, but it is not fatal.