Deletions occur when touching nucleotides are removed.
It occurs when a sequence of DNA is lost during DNA replication. Similar to insertions it can be small or a large. A single base can be lost or a full chromosome. This can occur because of mishaps of crossing over in meosis.Deletions are cause of some serious genetic diseases. There are three types of deletions.a microdeletion is a small deletion. Interstitial deletions occur in the interior of a chromosome. Terminal deletions occur at the end of a chromosome. Smaller deletions are not as dangerous as larger ones. Microdeletions are more common in children causing physical abnormalities. An example of a terminal deletion is the removal of the short arm of chromosome 5. This causes a disese called chri du chat syndrome. This syndrome occurs in newborns and has many symptoms such as a high pitched cry, slow growth, small
head. Many inversions play a part in human disease. Inversions involve the relocation of genetic material in a chromosome. A segment of a chromosome is removed, inverted and placed back into the same chromosome. In inversions, genetic material is neither gained or lost but just rearranged. There are two types of inversions. The two types are distinguished by whether or not the centromere is part of the segment which is inverted in the chromosome. The two types are called paractentric inversions and paricentric inversions. Paracentric inversions does not involve the centromere while the paricentric inversions do involve the centromere. A hetrozyhous person with the inversion causes overproduction of chromatids which leads to fertility problems. Translocations occur when a piece of a sequence is moved to another spot in the DNA sequence. Translocations can be either unbalanced or balanced. Unbalanced translocations means an unequal amount of DNA is transfered, while in balanced translocations equal amounts of DNA is transfered. People with balanced translocations may not notice it but people with unbalanced translocations are affected.There are two types of translocations. Robertsian translocations occur when chromosomes attach while a reciprocal translocation occurs when two pieces of two chromosomes break. Translocations like the other structural types are disease causing. A big one would be down syndrome, trisomy 21.This is a robetronian translocation. In this way a segment of chromosome 21 is re located on chromosome 15. However trisomy 21 is not always caused by this way.
Individuals with trisomy one suffer with physical abnormalities, lower immune systems and lower intellectual ability.