| visit: www.infertilitytutorials.com |
|
Deletions, Duplications and Isochromosomes
Deletions occur when a segment of a chromosome is lost altogether. Except for deletions that involve the sex chromosomes (the X and the Y chromosomes), deletions that involve more than a very small segment (even small segments contain multiple genes) are usually lethal mutations. Duplications occur when there is an extra chromosome segment. Extra genetic material may also result in lethal mutations, but generally result in less abnormalities than comparable sized deletions. An isochromosome results in either duplication of the short arm with deletion of the long arm of a chromosome or visa versa (duplication of the long arm with deletion of the short arm of a chromosome). Since isochromosomes are missing an entire arm of the chromosome, these are often lethal mutations unless they involve the loss of the short arms of an acrocentric chromosome (such as with Robertsonian translocations). | |||||||||||||
