What are chromosomal/genetic abnormalities?

There are many types of chromosome abnormalities. However, they can be organized into two basic groups: numerical abnormalities and structural abnormalities.

  • Numerical Abnormalities: When an individual is missing one of the chromosomes from a pair, the condition is called monosomy or when an individual has more than two chromosomes instead of a pair, the condition is called trisomy.
    • Trisomies account for the most common genetic abnormalities – conditions such as Down’s syndrome (having a extra copy of chromosome 21), Patau’s syndrome (having a extra copy of chromosome 13) and Edward’s syndrome (having a extra copy of chromosome 18).
  • Structural Abnormalities: A chromosome’s structure can be altered in several ways.
    • Deletions: A portion of the chromosome is missing or deleted.
    • Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.
    • Translocations: A portion of one chromosome is transferred to another chromosome.
    • Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted.
    • Rings: A portion of a chromosome has broken off and formed a circle or ring.

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