Variation in Chromosome Structure and Number

Aneuploidy Conditions

1. Nullisomy - the loss of both pairs of homologous chromosomes; individuals are called nullisomics; chromosomal composition = 2N-2
2. Monosomy - the loss of a single chromosome; individuals are called monosomics chromosomal composition = 2N-1
3. Trisomy - the gain of an extra copy of a chromosome; individuals are called trisomics; chromosomal composition = 2N+1
4. Tetrasomic - the gain of an extra pair of homologous chromosomes; individuals are called tetrasomics; chromosomal composition = 2N+2
5. Double monosomic - the loss of one chromosome from each of two pair of homologous chromosome; chromosomal composition = 2N-1-1
6. Double tetrasomic - the gain of an extra pair of two pairs of homologous chromosomes; chromosomal composition = 2N+2+2