= Solution
\b[The normal patterns are A3, B2 and C4.] In each, two principal <DNA fluorescence in situ hybridization> signals lie at corresponding positions on the two replicated <sister chromatids>. A single <chromosome> in <mitosis> has already replicated its <DNA>, so a unique locus normally has one copy on each sister, rather than two signals because two homologous <chromosomes> are being shown.
The other examples show a single unresolved or missing partner signal, extra fragmented signals, or an abnormal distribution. The images are small and relative intensities differ, especially in row C, so the appropriate criterion is the paired principal locus signals at matching positions, not perfect equality of brightness. Counts from many <chromosomes>, adequate optical resolution and hybridization controls are necessary before classifying borderline examples.
Back to article page
