The dicentric chromosome may be pulled apart during mitosis, with a random loss or gain of genetic material. The results of a pericentric inversion going through meiosis, with a recombination within the inversion is shown in figure 11. Again, four different gametic products are produced, one normal, one has the inversion, and two have duplicated portions and deleted portions. The effect on the phenotype is almost always deleterious, but the magnitude of the effect depends upon the size of the duplications and deletions, and where they occur. When a telomere is lost there is a strong tendency for the chromosome to unite with a similar fragment lacking a telomere.
Ring chromosomes cause no problem until there is a sister chromatid exchange.
Sister chromatid exchange is a rather common mitotic event. It can be detected in five or six chromosomes at each mitotic division Since the two chromatids are identical in all respects, there is no gain or loss of genetic material. However, when a sister chromatid exchange occurs in a ring chromosome, a double chromatid is produce that is dicentric. Dicentric rings have the same problem going through mitosis as the dicentric chromosomes of paracentric inversions. When the two centromeres line up on opposite sides of the metaphase plate, they migrate to opposite poles, and the chromosome is randomly broken, with loss or gain of genetic material.