First, refresh your memory about the cell and basic cell biology.
Then review the genome.
DNA is found in the nucleus
And in the mitochondria. Mitochondrial DNA is circular and carries the information for 37 genes. Almost all (99.9%) of your mitochondrial DNA is inherited from your mother.
DNA is transcribed into mRNA in the nucleus, and translated into protein in the cytoplasm.
A gene is the functional unit of heredity in an organism. A gene's nucleotide sequence encodes an RNA or polypeptide.
A gene mutation is a heritable change in the DNA sequence that makes up a gene.
A point mutation are those mutations that affect a single base pair of DNA. It occurs when 1 base on a DNA strand is replaced with a different one. There are four types of point mutations:
(1) missense mutation is where the point mutation results in a wrong codon and a wrong amino acid.
(2) nonsense mutation is where the point mutation results in a stop codon where the protein would be terminated at that point.
(3) silent (or sense) mutation is where the point mutation results in a new codon that still encodes the same amino acid
(4) frameshift mutation results from the addition or deletion of a base pair in a gene. Such additions or deletions shift the mRNA's reading frame by one base so that incorrect amino acids are added to the protein chain.
A chromosomal mutation occurs when a long segment of DNA is deleted, inserted, inverted or translocated.
Much more can be learned about the human genome at this Wellcome Trust website.