Nullisomy

Content
Numerical Changes in Chromosomes
Aneuploidy 
Monosomy
Nullisomy
Trisomy
Tetrasomy
Euploidy 
Monoploidy and haploidy
Polyploidy

Nullisomics are those individuals, which lack a single pair of homologous chromosomes, so that the chromosome formula would be 2n - 2 and not 2n - 1 - 1, which would mean a double monosomic. Sears had isolated all the 21 nullisomics in wheat.