Northern blot
The northern blot is a technique used in molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

 research to study gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 by detection of RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 (or isolated mRNA) in a sample. With northern blotting it is possible to observe cellular control over structure and function by determining the particular gene expression levels during differentiation, morphogenesis
Morphogenesis , is the biological process that causes an organism to develop its shape...

, as well as abnormal or diseased conditions. Northern blotting involves the use of electrophoresis
Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...

 to separate RNA samples by size and detection with a hybridization probe
Hybridization probe
In molecular biology, a hybridization probe is a fragment of DNA or RNA of variable length , which is used in DNA or RNA samples to detect the presence of nucleotide sequences that are complementary to the sequence in the probe...

 complementary to part of or the entire target sequence.