Mutations are changes in DNA that may or may not affect phenotype. Start by watching the Bozeman Science video, Mutations. 

There are many kinds of mutations that can occur during replication. 

• point mutation - simply substitutes one nucleotide for another
• frameshift mutation - inserts or deletes a nucleotide in the DNA sequence

Chromosomal mutations will affect many genes, and can occur during crossing over. Translocation results from the exchange of DNA segments between nonhomologous chromosomes. Chromosomal mutations tend to have a big effect!

Mutations in body cells do not affect offspring, but those in sex cells can be harmful or beneficial to offspring. 

Mutations can be caused by several factors including; replication errors, mutagens (UV rays, or chemicals, cancer drugs)