Genes are the simple genetic code that hides in the nuclei of the cells within living organisms. They are made up of four nucleic acids: adenine, cytosine, guanine, and thymine. They always pair up, and the pairs never change, though which side of the DNA they’re on can. Adenine will always pair up with thymine. Cytosine will always pair up with guanine.
This can change slightly when the DNA is being replicated since it is first encoded as RNA - a single stranded code piece. Thymine isn’t part of those bases, and is instead replaced by uracil.
The genes themselves are simply sections of DNA that code for certain things. The genes for blue eyes, for example, are different than the genes for brown eyes.
