ORTHERN/WESTERN BLOTS

The separation of DNA, RNA, and polypeptides based on size is a valuable biochemical technique that utilizes
migration through a gel to fractionate these macromolecules. For instance, DNA bands in an electrophoretic gel
form if many DNA molecules are of the same size, such as following a PCR reaction or restriction digestion of a
plasmid. However, in other scenarios, like after restriction digestion of chromosomal (genomic) DNA, there will be
a multitude of differently sized fragments in the digest, resulting in a continuous smear of DNA on a gel lane
instead of distinct bands.
In cases involving genomic DNA, additional techniques are necessary to detect the presence of a specific DNA
sequence within the smear of DNA separated on an electrophoretic gel. This detection can be achieved using a
DNA sequence probe, a method known as "Southern Blot." In this chapter, we will explore Northern Blots (for
RNA) and Western Blots (for proteins), which employ similar principles to detect respective macromolecules.

Gel Electrophoresis copie 1

Gel electrophoresis is a technique used to separate DNA fragments (or other macromolecules, such as RNA and
proteins) based on their size and charge. Electrophoresis involves running a current through a gel containing
molecules of interest. Based on their size and charge, the molecules will travel through the gel in different
directions or at different speeds, allowing them to be separated from one another.
All DNA molecules have the same amount of charge per mass. Because of this, gel electrophoresis of DNA
fragments separates them based on size only. Using electrophoresis, we can see how many different DNA
fragments are present in a sample and how large they are relative to one another. We can also determine the
absolute size of a piece of DNA by examining it next to a standard "yardstick" made up of DNA fragments of known
sizes.

DNA Cloning

When you hear the word “cloning,” you may think of the cloning of whole organisms, such as Dolly the sheep. However, all it means to clone something is to make a genetically exact copy of it. In a molecular biology lab, what’s most often cloned is a gene or other small piece of DNA

OBSERVING INTACT CHROMOSOMES

Visual observation of animal chromosomes provides valuable information in various studies. This chapter focuses on two techniques: bright-field microscopy and fluorescence in situ hybridization (FISH). Although the examples discussed here are specific to humans, these methods can be applied to study chromosomes in any organism, including animals.