Structural Rearrangements

Chromosomal structure abnormalities

chromosome breakage due to internal or external clastogens

could be correctly repaired most of the time

results as incorrect DNA repair

Interchromosomal rearrangements

translocations

dicentric chromosomes

insertion

intrachromosomal rearrangements

deletions

inversions

ring chromosomes

reciprocal translocations

balanced translocation

balanced exchanges between 2 or more chromosomes

no genetic material lost

ex (46,XX,t(8;21)(q22;q22)

Robertsonian translocations

unbalanced translocation

fusion in centromere region between 2 acrocentric chromosomes

may be phenotypically normal

ex 46,XY,+rob(13;14)(p10;q10)

Nonreciprocal translocation

unbalanced translocation

results from unbalanced exchange of genetic material between 2 or more ch

ch material is either lost or gained.

Dicentric chromosomes

unbalanced translocation

ch contain 2 centromeres

will result in abnormal mitoses with anaphase bridge or lagging ch

anaphase bridge in each centromere of dicentric migrate to opposite poles of spindle

Insertion

unbalanced translocation

Deletions

result in loss of ch material. monosomy of region of ch deleted

terminal deletions

result of one break with loss of acentric fragment during cell division due to anaphase lag

interstitial deletion

result from 2 breaks within same chromosome arm.

acentric fragment lost during cell divisions

Inversions

result when 2 breaks occur in same ch

middle segment rotates 180° before repair

results in no net loss of genetic material but change gene order

Pericentric inversions

One break in short arm one break in long arm

most constitutional pericentric inversions do not affect phenotype of carrier

does include centromere

nonviable

should be treated similarly to balanced reciprocal translocation in terms of risk of abnorm offspring

ex 46,XX,inv(8)(p23.1q22.1)

paracentric inversions

occur when both breaks are in same arm of chromosome

centromere not involved in version

meiosis inverted ch must form loop in region of inversion in order to pair with norm homolog

ex inv(3)(q21q26.2)

products are either acentric or dicentric

risk for offspring is negligible

duplications

occur when portion of ch material is duplicated

results in functional trisomy for segment of DNA

duplicated material may be inserted in same order or my be inverted

ex 46,XY,dup(12)(q13q22)

Isochromosome

formed when misdivision of centromere

occasionally centromere will divide horizontally resulting in one daughter cell with 2 sister chromatic of short arm and other daughter cell of long arm

during s phase centromere as well as long and short arm will be duplicated

one arm of isochromosome is mirror image of other

cell with isochromosome is trisomic for one ch arm and monosomic for other arm

Ring chromosomes

formed when 2 terminal breaks occuring on same ch

breaks form union causing continuous DNA molecule with one centromere

highly unstable either break or lag behind during anaphase