A reciprocal translocation is a chromosome anomaly where two chromosomes from different pairs swap part of their genetic material with each other. For example, a 13th chromosome could exchange genetic material with a 16th chromosome. In many cases, reciprocal translocations do not cause health problems, but can result in a reduction in fertility. Certain kinds of translocations have been linked with medical issues, such as increased susceptibility to mantle cell lymphoma in people who have a reciprocal translocation between a 14th and 11th chromosome.
This occurs during meiosis, the process where chromosomes mix genetic material to create a set of varied daughter cells, ensuring a mixture of traits are passed on to offspring. In healthy meiosis, chromosomes only swap genetic material with chromosomes in the same pair. In a reciprocal translocation, material jumps between chromosomes in separate pairs, creating what are known as derivative chromosomes. Depending on the material swapped, the daughter cell may be able to successfully fuse with another daughter cell to create a zygote that becomes a carrier of the translocation, or the cell may be useless for reproduction, making it infertile.
In a balanced reciprocal translocation, the same amount of material is swapped between chromosomes. Unbalanced translocations involve segments of differing lengths from each chromosome. These are more likely to cause infertility and are also more likely to lead to health problems; if one chromosome in a pair is shortened and the other has a deleterious gene, the gene may express because a corresponding healthy section of chromosome to override it is missing.
Some reciprocal translocations are linked with congenital disorders, especially in cases where people with translocations reproduce and pass on defective chromosomes to their offspring. Others may not be noticed, and in some cases can even contribute an evolutionary benefit. The ability to exchange and shuffle genetic material during sexual reproduction has been valuable for a wide variety of species, and occasionally translocations may confer an advantage.
Signs of a reciprocal translocation can be uncovered during genetic testing, when one or more chromosomes may appear abnormal or there is a sequence on a chromosome that clearly does not belong. People with translocations who have trouble conceiving can discuss their options with a fertility specialist. It may be possible to use assisted reproduction to successfully fertilize an egg, or options like donor eggs or sperm may need to be considered to achieve a healthy pregnancy.