There are many ways that some of your genes can be changed, and there are 3 main mutations:

Substitution:
One Nucleotide has changed from one to another, Ex. C turned into G

Insertion:
Extra nucleotides are added to the sequences.

Deletion:
A nucleotide has been removed

Frame Shift Mutations:
Insertion and Deletion both cause the entire sequence to shift in either direction, as new amino acids form.
It will almost always change the entire sequence.

Stop Codon Exception:
A deletion or insertion at the end of the sequence could potentially not have an effect, because there are multiple stop codons, however, it is very unlikely.

Proto-oncogenes:
A group of genes that cause normal cells to become cancerous when they are mutated.

Tumor suppressor:
Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die.

Point Mutation:
A mutation happens when ONE nucleic acid is changed.
There are NONE added or removed, they are just CHANGED

Silent: The mutation doesn’t change the protein outcome

Nonsense: The mutation turns the codon into a stop codon

Missense: The codon/protein is changed

Genome:
ALL of your DNA that you are born with.

Epigenetics:
What genes are activated/turned on
Modification in gene expression, like operons

In Eukaryotic cells, operons are not present but there are TWO main gene expression modifications:

Histone Modification:
When the histone is tightly packed around the DNA the genes are not accessible, but when the histones open up genes can be activated.

Methylation:
When a methyl group or epigenetic factor tags DNA to activate or repress certain genes.
The process is NOT permanent, so it can be changed in different environments.

Methyl groups / Epigenetic Factor:
Can bind to a histone and either open them up OR fold them tight in.