DNA fragments are not typically exposed to an alkaline solution before hybridization. In fact, doing so would be detrimental to the process.

Here's why:

* Alkaline solutions denature DNA: High pH solutions (alkaline) break the hydrogen bonds that hold the two strands of DNA together, leading to single-stranded DNA. While this might seem useful for hybridization, it would also denature the probes used in the process, rendering them ineffective.

* Hybridization relies on single-stranded DNA: Hybridization occurs between complementary single-stranded DNA molecules. However, the denaturation process needs to be carefully controlled.

Here's how the process typically works:

1. DNA is denatured: DNA is heated to a high temperature (typically around 95°C) to break the hydrogen bonds and separate the strands.

2. Hybridization: The denatured DNA (target DNA) is then cooled slowly, allowing complementary strands of probes to anneal (hybridize) to the target sequences.

3. Alkaline treatment (optional): *After* hybridization, some protocols use a mild alkaline solution to remove unbound probes.

Therefore, alkaline treatment is not used before hybridization but can be used in certain steps after hybridization for washing and removal of unbound probes.