Mutation: Change in DNA.
Germinal mutation occurs during formation of an egg or sperm.
Somatic mutation occurs when the change occurs after conception.
Chromosomal aberration occurs when the number and physical structure of chromosomes are altered.
Nondisjunction: The embryo has too many or too few chromosomes as a result of failure of chromosome pairs to separate in the dividing cell (meiosis). When this type of error occurs it is called aneuploidy. There are 3 types of aneuploidy:
Monosomy: only one member of a pair of chromosome is present
Trisomy: 3 chromosomes are present instead of 2
Polysomy: a chromosome is represented 4 or more times.
Translocation or inversion: rearrangement of chromosome arms.
Inversion: chromosome region becomes reoriented 180° out of its location. Same genetic material is present but the order of arranged is aberrant. Affect phenotype severely or not.
Deletions: part of chromosome is omitted. Phenotype is altered.