Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy. All affected individuals experience cognitive delays, but the intellectual disability is usually mild to moderate.
Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy. This condition is most often caused by trisomy 21. Trisomy 21 means that each cell in the body has three copies of chromosome 21 instead of the usual two copies.
A type of mutation in which a portion of a genetic material or a chromosome is duplicated or replicated, resulting in multiple copies of that region. Supplement Duplication results from an unequal crossing-over between misaligned homologous chromosomes during meiosis.
Such an event creates a chromosomal mutation called an inversion. Unlike deletions and duplications, inversions do not change the overall amount of the genetic material, so inversions are generally viable and show no particular abnormalities at the phenotypic level.
The four main types of chromosomal mutations are deletion, duplication, inversion and translocation. A fifth chromosomal mutation is known as a deficiency. This occurs when a chromosome is lost sometime during fertilization or development of a fetus. A deletion is the loss of a chromosomal fragment ...