Base pairing rules are like the special matching rules for the building blocks of DNA.

In simple terms:

• Adenine (A) always pairs with Thymine (T)
• Guanine (G) always pairs with Cytosine (C)

These rules are really important for two main things: making new DNA and fixing it when it's broken.

But sometimes, things can go wrong:

• Errors During Replication: If the pairs don't match up correctly, it can cause mistakes. These mistakes can make the cells not work like they should.

• Repair Mechanism Strain: If DNA gets damaged, the tools that fix it can get overwhelmed. When this happens, it can make DNA unstable.

To help with these problems, living things have special repair systems.

Some of these are:

• Nucleotide Excision Repair: This is like a spell-check for DNA, looking for mistakes and fixing them.
• Proofreading by DNA Polymerases: These are like quality controllers making sure everything is right as new DNA is made.

Even with these systems, sometimes they can struggle, especially when put under a lot of stress.