Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies. Inheritance
Most chromosome abnormalities occur as an accident in the egg cell or sperm, and therefore the anomaly is present in every cell of the body. Some anomalies, however, can happen after conception, resulting in Mosaicism (where some cells have the anomaly and some do not). Chromosome anomalies can be inherited from a parent or be "de novo". This is why chromosome studies are often performed on parents when a child is found to have an anomaly. If the parents do not possess the abnormality it was not initially inherited; however, it may be transmitted to subsequent generations. Acquired chromosome abnormalities
Most cancers, if not all, could cause chromosome abnormalities, with either the formation of hybrid genes and fusion proteins, deregulation  of genes and overexpression of proteins, or loss of tumor suppressor genes (see the "Mitelman Database"  and the Atlas of Genetics and Cytogenetics in Oncology and Haematology,). Furthermore, certain consistent chromosomal abnormalities can turn normal cells into a leukemic cell such as the translocation of a gene, resulting in its inappropriate expression. DNA damage during spermatogenesis
During the mitotic and meiotic cell divisions of mammalian gametogenesis, DNA repair is effective at removing DNA damages.
Controversy over use
There remains controversy over the use of RAD as an unofficial diagnosis. With its use not only being limited to clinical lexicon, but also transitioning to clinical literature now, more physicians are now increasingly disapproving its use in the healthcare setting.One of the largest problems with the using RAD as a diagnostic label lies in the ambiguity of its meaning, as RAD has no true clinical definition. It is either not listed or redirects to "asthma" in all major medical journal or website. In addition to that, it is also not recognized in the American Academy of Pediatrics; the American Thoracic Society; or the National Heart Lung and Blood Institute. In addition, treatments for asthma, chronic bronchitis, emphysema, or pneumonia may not be prescribed under a label of reactive airway disease. In contrast, some physicians also fear overtreatment for RAD, as patients can be prescribed inhaled beta-agonists or inhaled corticosteroids, which are medications used for asthma. If an individual with RAD doesnt have asthma, there is no evidence these treatments are beneficial. As a result of its ambiguous place in the medical field, the symptoms used to characterize it are often inconsistent and can lead to confusion in a healthcare setting.