What is Hybridization?

As we have already seen, under normal conditions, the DNA molecule is composed of two strands. These two strands are connected by hydrogen bonds, and together form the well-known double helix structure. When a solution containing DNA is heated, these hydrogen bonds disappear, and the two strands drift apart. This single-stranded DNA is called denatured DNA (or, surprisingly enough single-stranded DNA). When the solution is cooled, hydrogen bonds form between matching bases in the strands. These bonds are formed in places where a match (or at least a partial match) exists. If these bonds begin to form in corresponding parts of two strands, they will quickly completely join and the double-helix will reappear. However, this is not guaranteed to happen. Bonds can form even between strands of different DNA molecules or strands of different length. Consider a heated solution of some target DNA molecule. Let us take short single-stranded chains of nucleotides, called oligonucleotides (or oligos for short), that we have synthesized and add them to the solution. Each oligo is a known nucleotide sequence between 10 and 12 bases long. Now, when the solution is cooled, the oligos will stick to parts of the target which contain a DNA sequence complementary to that of the oligo. The resulting composition is called hybrid DNA. Each oligo thus probes for the presence of its complementary sequence, and indeed oligos are called probes