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Trisomy 13/18 Info

Chromosome defects, what are they?

There are 22 pairs of chromosomes, numbered 1-22 in order of size, and a pair of sex chromosomes, XX in females and XY in males, making a total of 46 chromosomes in each normal human cell. 


The tri in the word trisomy means three. In each cell there is one set of three identical chromosomes among the normal pairs.

Results of Chromosome Tests


Genetics is the study of human cells, and a Clinical Geneticist will interpret the results of chromosome tests taken from blood, skin, bone marrow, or connective tissue. When tests during pregnancy have shown a chromosome abnormality the clinical geneticist, if consulted, will discuss the results with the family.

Related Disorders

The degree of the medical problems and disability can vary widely in children with a related disorder because the genetic material that is extra or missing will be different in every case, and the professional opinion of a clinical geneticist should always be sought.