Biotechnology

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Direction of movement of strands

Detector

Last base of longest labeled strand

Last base of shortest labeled strand

Slide 62

Analyzing Gene Expression

Nucleic acid probes can hybridize with mRNAs transcribed from a gene

Probes can be used to identify where or when a gene is transcribed in an organism

Slide 63

Studying the Expression of Single Genes

Changes in the expression of a gene during embryonic development can be tested using

Northern blotting

Reverse transcriptase-polymerase chain reaction

Both methods are used to compare mRNA from different developmental stages

Slide 64

Northern blotting combines gel electrophoresis of mRNA followed by hybridization with a probe on a membrane

Identification of mRNA at a particular developmental stage suggests protein function at that stage

Slide 65

Reverse transcriptase-polymerase chain reaction (RT-PCR) is quicker and more sensitive

Reverse transcriptase is added to mRNA to make cDNA, which serves as a template for PCR amplification of the gene of interest

The products are run on a gel and the mRNA of interest identified

Slide 66

Fig. 20-13

TECHNIQUE

RESULTS

Gel electrophoresis

cDNAs

-globin gene

PCR amplification

Embryonic stages

Primers

1 2 3 4 5 6

mRNAs

cDNA synthesis

1

2

3

Slide 67

In situ hybridization uses fluorescent dyes attached to probes to identify the location of specific mRNAs in place in the intact organism

Slide 68

Fig. 20-14

50 µm

Slide 69

Studying the Expression of Interacting Groups of Genes

Automation has allowed scientists to measure expression of thousands of genes at one time using DNA microarray assays

DNA microarray assays compare patterns of gene expression in different tissues, at different times, or under different conditions

Slide 70

Fig. 20-15

TECHNIQUE

Isolate mRNA.

Make cDNA by reverse transcription, using fluorescently labeled nucleotides.

Apply the cDNA mixture to a microarray, a different gene in each spot. The cDNA hybridizes with any complementary DNA on the microarray.