Cytogenetic and FISH Techniques

Cytogenetic techniques examine chromosomes for numerical and structural abnormalities, while fluorescence in situ hybridization (FISH) uses labeled DNA probes to light up specific sequences directly within cells or on chromosome spreads. Together they bridge whole-chromosome analysis and sequence-specific molecular detection.

Definition

Cytogenetic and FISH techniques are methods that detect and localize chromosomal abnormalities and specific DNA sequences within cells, with FISH using fluorescently labeled nucleic acid probes that hybridize to complementary target sequences.

Scope

The topic covers conventional karyotyping, FISH for locus- and chromosome-specific probes, and comparative genomic hybridization for genome-wide copy-number assessment. It treats these as methodological reference material on how chromosomal and sub-chromosomal changes are visualized, not as clinical testing guidance.

Key concepts

• Karyotyping
• Fluorescence in situ hybridization (FISH)
• Locus-specific and centromeric probes
• Chromosomal rearrangements and aneuploidy
• Comparative genomic hybridization (CGH)
• Copy-number gains and losses
• Interphase versus metaphase analysis

Mechanisms

Conventional cytogenetics arrests dividing cells in metaphase, spreads and stains the chromosomes, and reads the banding pattern to detect numerical and structural abnormalities. FISH instead applies fluorescently labeled single-stranded DNA probes that hybridize to their complementary target sequences in fixed cells; the bound probe is visualized by fluorescence microscopy, localizing a sequence to a chromosome or interphase nucleus (Pinkel et al., 1986). Comparative genomic hybridization extends this principle to the whole genome by co-hybridizing differentially labeled test and reference DNA and comparing their fluorescence ratios to map copy-number gains and losses (Kallioniemi et al., 1992).

Clinical relevance

These techniques are used to detect chromosomal abnormalities and structural rearrangements relevant to constitutional and acquired disorders. This entry describes how the methods visualize chromosomes and sequences as a reference; it does not provide guidance on ordering or interpreting any specific cytogenetic test in patient care.

Evidence & guidelines

The methods rest on foundational primary studies that introduced high-sensitivity fluorescence hybridization (Pinkel et al., 1986) and comparative genomic hybridization for solid tumors (Kallioniemi et al., 1992). Detailed assay and reporting standards are maintained by professional cytogenetics bodies and are referenced in laboratory practice.

History

Human cytogenetics matured in the mid-twentieth century with reliable chromosome counting and banding. The introduction of quantitative, high-sensitivity fluorescence in situ hybridization in 1986 added sequence-specific resolution to chromosome analysis (Pinkel et al., 1986), and comparative genomic hybridization in 1992 made genome-wide copy-number surveys possible (Kallioniemi et al., 1992), foreshadowing today's array- and sequencing-based copy-number methods.

Key figures

• Daniel Pinkel
• Joe W. Gray
• Anne Kallioniemi

Seminal works

• pinkel-1986
• kallioniemi-1992

Frequently asked questions

What does FISH add to conventional karyotyping?

Karyotyping shows whole chromosomes and large structural changes, while FISH uses labeled probes to detect specific sequences or rearrangements, including in non-dividing interphase cells where a full karyotype cannot be made.

How does comparative genomic hybridization detect copy-number changes?

It co-hybridizes differentially labeled test and reference DNA to the same target and compares their fluorescence ratios; regions where the test signal is relatively higher or lower indicate genomic gains or losses.