The introduction of FISH techniques has been a valuable tool in the identification of marker chromosomes. Structural abnormalities involve changes in the structure of one or more chromosomes. The effects are typically severe since there is a loss of genetic material. Although an inversion carrier may be completely normal, they are at a slightly increased risk for producing a chromosomally unbalanced embryo. This is because an inverted chromosome has difficulty pairing with it's normal homolog during meiosis, which can result in gametes containing unbalanced derivative chromosomes if an unequal cross-over event occurs.
Translocations involve exchange of material between two or more chromosomes.
Problems arise with translocations when gametes from a balanced parent are formed which do not contain both translocation products. When such a gamete combines with a normal gamete from the other parent the result is an unbalanced embryo which is partially monosomic for one chromosome and partially trisomic for the other. Sometimes individuals are found who have both normal and abnormal cell lines. These people are called mosaics and in the vast majority of these cases the abnormal cell line has a numerical chromosome abnormality. Structural mosaics are extremely rare.