File:Trisomy21female.jpg

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Trisomy 21 (Down Syndrome) Female Karyotype

Down syndrome or trisomy 21 is caused by nondisjunction of chromosome 21 in a parent who is chromosomally normal and is one of the most common chromosomal abnormalities in liveborn children. The frequency of trisomy 21 in the population is approximately 1 in 650 to 1,000 live births, in Australia between 1991-97 there were 2,358 Trisomy 21 (Down) infants.

  • The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes.
  • The karyotype is the characteristic chromosome complement as identified by staining and can only be identified during cell division when chromosomes are folded.
  • The chromosomes when organised as an image in sequence are called a karyogram or idiogram.


Trisomy 21 Links: Trisomy 21 | Image T21 female karyotype | Image T21 male karyotype | chromosome 21 | Category:Trisomy 21 | Genetic Abnormalities | Prenatal Diagnosis

Chromosome 21

  • the smallest human chromosome
  • about 47 million base pair
  • about 1.5 % of the total DNA in cells
  • contains between 300 and 400 genes (of human estimated 20,000 to 25,000 total genes)
  • trisomy 21 or Downs Syndrome - additional copy of this chromosome
  • partial monosomy 21 - missing segment of the chromosome in each cell
  • ring chromosome 21 - circular structure, occurs when there are two breaks in a chromosome and the ends of the chromosome then fuse together



Cite this page: Hill, M.A. (2019, April 20) Embryology Trisomy21female.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Trisomy21female.jpg

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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current16:19, 27 July 2009Thumbnail for version as of 16:19, 27 July 2009480 × 284 (12 KB)MarkHill (talk | contribs)Down syndrome or trisomy 21 is caused by nondisjunction of chromosome 21 in a parent who is chromosomally normal and is one of the most common chromosomal abnormalities in liveborn children. The frequency of trisomy 21 in the population is approximately 1
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