Definition

Noun: A chromosomal abnormality characterized by the presence of three copies of a particular chromosome, instead of the normal two copies (one from each parent), in a cell.

Usage

Trisomy is a medical and genetic term. It is typically followed by a number indicating the specific chromosome involved (e.g., trisomy 21). It refers to a condition present from conception.

Examples

• General Use:
  • Down syndrome is caused by trisomy 21.
  • Prenatal testing can screen for common trisomies.
  • The genetic counselor explained that a trisomy occurs due to nondisjunction during cell division.

Advanced Usage

• "Full trisomy": When all cells in the body have three copies of the chromosome.
  • The diagnosis was a full trisomy 18, a very serious condition.
• "Mosaic trisomy": When only some of the body's cells have the extra chromosome.
  • The milder symptoms were explained by the presence of a mosaic trisomy.
• "Partial trisomy": When only a segment of the chromosome is present in triplicate.
  • The abnormality was identified as a partial trisomy of the long arm of chromosome 5.

Variants and Related Words

• Trisomic (adjective): Relating to or characterized by trisomy.
  • The fetus was diagnosed with a trisomic condition.
• Monosomy (noun): The opposite condition, having only one copy of a particular chromosome.
• Aneuploidy (noun): The general term for an abnormal number of chromosomes, which includes trisomy.

Synonyms

• Chromosomal trisomy (more formal specification)
• Triploidy of a chromosome (technical, less common; note: Triploidy usually refers to three complete of chromosomes)

Notes on Meaning

The core meaning is strictly genetic. It does not refer to symptoms or syndromes themselves (like Down syndrome), but to the specific chromosomal cause of those conditions. The severity of effects varies greatly depending on which chromosome is involved.

Noun

1. chrosomal abnormality in which there is one more than the normal number of chromosomes in a cell