When a structural chromosome abnormality is found in a fetus, the parents chromosomes should be karyotyped to see if they carry a balanced rearrangement or the same rearrangement or whether the abnormality in the fetus arose de novo.

In general, de novo rearrangements carry a greater risk of abnormality than inherited ones.

Some familial ones arise in meiosis after a centric fusion between satellited chromosomes (50% involve 15 p which can be identified by DAPI distamycin A staining).

If the marker contains only repetitive and r DNA, there will be no clinical consequence.

mat = maternally derived; pat = paternally derived.

Structural chromosome abnormalities include breaks in chromosome arms.

Their offspring with a duplication or deletion will have trisomy or monosomy. These are small (unidentified) chromosomes with a centromere and may be of no consequence if they are "familial" but if they arise de novo in a fetus they may cause congenital anomalies.

They are small, usually metacentric, fragments sometimes detected during routine karyotyping.

(A balanced translocation carrier can never have a normal child.).Some rearrangements where there is no apparent loss of genetic material would be expected to be innocuous in the bearer, however, they turn out to be a problem during meiosis.