Chromosome Mutation: Balanced Structural Rearrangements

such rejoining occurs within a chromosome, a chromosome segment between the two breakpoints becomes inverted and is thus called an inversion. If the rejoining of broken chromosome ends involves two chromosomes, two abnormal chromosomes result: each consists of a part derived from the other chromosome and lacks a part of itself. These are referred to as translocations.

As long as the translocations result in no loss of genetic material, the cells seldom harbor any biological abnormalities. Offspring resulting from a germ cell (egg or sperm) bearing a translocation will also exhibit no abnormalities, if the translocation is of a balanced type. However, during germ-cell formation in the translocation-bearing individuals, the proper distribution of chromosomes in the egg or sperm occasionally fails, resulting in miscarriage, malformation, or mental retardation of the offspring.

It has been recognized that one of the causes of infertility is that one partner is a translocation carrier.