Validation of isochromosomes and the Chromosome 22 inversion (inv22) by FISH. Cohybridization on metaphases from prep2.1A of BAC clones CH271-162A04 (red) and CH271-113K11 (blue) on Chromosome 14 and CH271-74O21 (red) and CH271-119L09 (green) on Chromosome 22. A wild-type Chromosome 14 exhibits one red hybridization signal on 14p and one blue signal on 14q. i(14p) shows two red signals on the same chromosome, and i(14q) shows two blue signals on the same chromosome. Similarly, the wild-type Chromosome 22 displays a centromere red–green signal pattern, whereas an inverted Chromosome 22 shows a centromere green–red signal pattern. This experiment confirms the presence of a supernumerary isochromosome i(14p)/i(14q) and demonstrates the presence of the inversion on Chromosome 22 in a heterozygous state but only in metaphases in which i(14q) is present. (A) FISH image of a metaphase with i(14q) and inversion on Chromosome 22 in a heterozygous state. (B) FISH image of metaphase with i(14p) and no Chromosome 22 inversion.