Variations in the number of chromosomes in humans: aneuploidy

Aneuploidy is a chromosomal anomaly, characterized by a variation in the normal number of chromosomes present within a cell of a given species.

As far as the human being is concerned, a subject having more or fewer chromosomes than the normal number which is 46 is considered aneuploid .

Aneuploidy can affect autosomal chromosomes or sex chromosomes and can sometimes cause serious consequences. One of the best known aneuploidies is Down syndrome (or trisomy 21 ), which is characterized by the presence of another autosomal chromosome 21 in addition to the two canons.

Other fairly well-known autosomal aneuploids are: trisomy 13 (or Patau syndrome) and trisomy 18 (or Edwards syndrome). Among the sexual aneuploidies, on the other hand, we note: Turner syndrome (exclusive of the female sex and characterized by the lack of an X chromosome) and Klinefelter syndrome (exclusive of man and marked by the presence of one or more X chromosomes).