Question

How harmful are non-reciprocal translocations?

Answer 1

Translocation is a type of chromosomal abnormality. It is a change in position of a chromosomal segment to another region of the same chromosome or different chromosome. Non-reciprocal translocation is a type of translocation and different from reciprocal translocation. It is a one-way transfer of a chromosomal segment from a non-homologous chromosome to the other chromosome.

Complete answer:
Non-reciprocal translocation is dangerous if it leads to production of a chromosome with two chromatids (dicentric chromosome).
Two centromeres of one sister chromatid in the next mitosis can become attached to the opposite spindle poles. This arrangement causes the chromatid to get torn into two, when an elongation of the spindle in anaphase occurs. This produces a pair of broken DNA ends, which fuses with other broken ends, producing more translocation. This leads to another round of chromosome fusion and breakage.
These events are referred to as breakage-fusion-bridge cycles, which will continue indefinitely, which generate all types of chromosomal translocations. This results in amplification or loss of larger chromosomal regions.
There are two genetic consequences. If a segment is inserted between two genes, linkage distance between the two genes increases. Also, the genes found on the insertional segment will be nearer to the genes in the region, in which it was inserted. This defines new linkage relationships among those genes.

Note:
Reciprocal translocation is the most common type of translocation. It occurs when chromosomal segments are exchanged between two non-homologous chromosomes. Two chromosomal segments participate in reciprocal translocation, whereas only one chromosomal segment is involved in non-reciprocal translocation. Both are types of interchromosomal translocation and both structural rearrangements lead to massive changes in genome and thereby, mutation occurs.