Simple question and answers: Fluorescence in situ hybridisation (FISH)

1.Which of the following statements about FISH probes is false?

Alpha satellite probes bind to centromeric repetitive DNA sequences

Beta satellite probes identify sequences present in only one copy number per chromosome

Unique sequence probes detect a specific chromosome region or gene

FISH probes are typically 100-200 kb in length

2.Which of the following components are required for FISH?

DNA polymerase

Agarose gel electrophoresis

Electron microscope

Labeled DNA probe

3. Which describes the correct order of events in FISH?

Visualisation, fixation, hybridization, denaturation

Fixation, visualization, denaturation, hybridization

Fixation, denaturation, hybridization, visualisation

Denaturation, fixation, hybridization, visualisation

4. The following image shows the result of FISH telomere screening. Which of these statements describes the correct result?

Result of FISH telomere screening 
© St George’s, University of London

Microdeletion 16q and duplication 9p

Microdeletion 16p and duplication 9q

Microdeletion 9p and duplication 16q

Microdeletion 9q and duplication 16p

Answres:-

1. B 

Beta satellite probes bind to repetitive sequences (like alpha satellite probes) on the p arms of the acrocentric chromosomes. They are useful in distinguishing the acrocentric chromosomes, which may not be distinguishable with alpha satellite probes. Unique sequence probes identify sequences present in only one copy number per chromosome.

2. D

A fluorescently-labelled DNA probe is used to bind the target DNA.

3. C

The metaphase chromosome preparations are fixed to the surface of a glass slide, the fluourescently-labeled probe is added and both the probe and chromosomes are denatured. Hybridization then occurs (the slide is usually incubated overnight- this depends upon the probe used as some probes take longer than others to hybridise). The slide is then washed to remove any unbound probe to avoid background noise and a fluorescent microscope is used to visualize the hybridized probes.

4. C

There are three signals from 16q and a single signal from 9p.