# DBT JRF 2020 — Question 93

Exam: DBT JRF 2020 · Section: B · Topic: Molecular Biology · Difficulty: Easy

## Question

The technique used to locate specific genes in chromosomes is

## Options

- **A.** western blotting
- **B.** in-situ hybridization
- **C.** dot blot technique
- **D.** colony hybridization

## Answer

Option B

## Explanation

Fluorescence In Situ Hybridisation (FISH): a cytogenetic technique for localising specific nucleic acid sequences within fixed cells or on chromosomes. Procedure: (1) Prepare fluorescently labelled DNA probe (complementary to target gene sequence); (2) Denature chromosomal DNA in metaphase spread; (3) Hybridise labelled probe to complementary chromosomal sequences; (4) Detect hybridisation signals by fluorescence microscopy. The fluorescent signal appears at the chromosomal location of the target gene. Multicolour FISH (m-FISH, spectral karyotyping) simultaneously paints all 24 human chromosomes in different colours. FISH is used for: chromosomal rearrangements, gene copy number, translocations, deletions, amplifications, gene mapping. Southern blotting detects DNA sequences in gel; Western detects proteins; colony hybridisation detects plasmid inserts; PCR amplifies sequences but doesn't localise them on chromosomes.

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