A change in the genetic material of a cell. Although the term often has a negative connotation, mutations (including polymorphisms) can be harmful, beneficial, or neutral in their effect on cell function.

There are two main types of mutations:

• Chromosomal Mutations: mutations that affect whole chromosomes and whole genes rather than just individual nucleotides
• Point Mutations (Nucleotide mutations): Gene mutation in which a single base pair in DNA has been changed

Chromosomal disorders

Non-disjunction: pairs of homologous chromosomes do not separate normally during meiosis. One gamete receives two of the same type of chromosome, and another gamete receives no copy

Change in chromosomal number

Aneuploidy: results from the fertilization of gametes in which nondisjunction occurred. Offspring with this condition have an abnormal number of a particular chromosome. Monosomic: only one copy of a chromosome. Trisomic: three copies of a chromosome.

Polyploidy: A condition in which an organism has more than two complete sets of chromosomes. Triploidy (3n) is three sets of chromosomes. Tetraploidy (4n) is four sets of chromosomes

Most popular types of mutations

• Substitution: one base is changed to a different base
• Frameshift Mutations: a mutation that shifts the reading frame of the genetic message by inserting or deleting a nucleotide
• Silent mutations: have no effect on the amino acid produced by a codon because of redundancy in the genetic code
• Missense mutations: still code for an amino acid, but not the correct amino acid
• Nonsense mutations: change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein