The four main types of chromosomal mutations are deletion, duplication, inversion and translocation. A fifth chromosomal mutation is known as a deficiency. This occurs when a chromosome is lost sometime during fertilization or development of a fetus.
A deletion is the loss of a chromosomal fragment. This causes genes to be lost in the fetus. A duplication mutation occurs when chromosomal fragments are doubled, resulting in duplication of genetic material. Inversion mutations occur when chromosomes change their original directions. During inversion, mutated chromosomes break and flip at their breakage point. Translocation mutations occur when nonhomologous chromosomes pair together. All these mutations can be harmful or benign depending on the chromosomes they affect.