Trisomy 18

Abstract

Introductory Glossory of Genetic Terms* Aneuploid(Y): A euploid cell has a balanced set of normal chromosomes. Euploid cells have 23 or a multiple of 23 chromosomes, for instance, 46, 69, or 92 chromosomes (haploidy, diploidy, triploidy, or tetraploidy, respectively). Aneuploid cells have a chromosomal number other than 23 or a multiple of 23 chromosomes. Autosomes, Autosomal Chromosomes: A normal cell has two sex chromosomes (XX, XY) and 44 autosomes. The autosomes are divided into seven groups according to size of the chromosome and site of the centromere (kinetochore). Each group consists of several pairs of autosomal chromosomes which are numbered from one to 22 according to the Denver Classification. In this article, D and E chromosomes are mentioned repeatedly. The group of the D chromosomes consists of the chromosomal pairs 13-15. The group of the E chromosomes consists of the chromosomal pairs 16-18. Deletion (p 602): Loss of a chromosomal