Genetic Terminology

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:

• 1. Monosomy: only one member of a pair of chromosome is present

  2. Trisomy: 3 chromosomes are present instead of 2

  3. 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.