can be numerical, as in the presence of extra or missing chromosomes, or structural, as in derivative chromosome, translocations, inversions, large-scale deletions or duplications. Numerical abnormalities, also known as aneuploidy, often occur as a result of nondisjunctionduring meiosis in the formation of a gamete; trisomies, in which three copies of a chromosome are present instead of the usual two, are common numerical abnormalities. Structural abnormalities often arise from errors in homologous recombination. Both types of abnormalities can occur in gametes and therefore will be present in all cells of an affected person's body, or they can occur during mitosis and give rise to a genetic mosaicindividual who has some normal and some abnormal cells.
Causes. X-ray temperature changes chemical reactions virus rubella virus rupees. Mustard gas.
Numerical disorders. Down syndrome 21 trisomy. Patau syndrome for trisomy 13. Edward syndrome trisomy 18 klinefelter syndrome x x y. Turner syndrome 45X.
Deletion cri du chat syndrome or angelman.
Inversion chromosome 9 infertility.
Translocation leukaemia, infertility or down syndrome when part of a chromosome goes to other chromosome.
isochromosome turner syndrome.
Duplication Charcot marie tooth disease duplication on chromosome 17.
Chromosomal abnormalities that lead to disease in humans include
Turner syndrome results from a single X chromosome (45,X or 45,X0).
Klinefelter syndrome, the most common male chromosomal disease, otherwise known as 47,XXY, is caused by an extra X chromosome.
Edwards syndrome is caused by trisomy (three copies) of chromosome 18.
Down syndrome, a common chromosomal disease, is caused by trisomy of chromosome 21.
Patau syndrome is caused by trisomy of chromosome 13.
Trisomy 9, believed to be the 4th most common trisomy, has many long lived affected individuals but only in a form other than a full trisomy, such as trisomy 9p syndrome or mosaic trisomy 9. They often function quite well, but tend to have trouble with speech.
Also documented are trisomy 8 and trisomy 16, although they generally do not survive to birth.
Some disorders arise from loss of just a piece of one chromosome, including
Cri du chat (cry of the cat), from a truncated short arm on chromosome 5. The name comes from the babies' distinctive cry, caused by abnormal formation of the larynx.
1p36 Deletion syndrome, from the loss of part of the short arm of chromosome 1.
Angelman syndrome – 50% of cases have a segment of the long arm of chromosome 15 missing; a deletion of the maternal genes, example of imprinting disorder.
Prader-Willi syndrome – 50% of cases have a segment of the long arm of chromosome 15 missing; a deletion of the paternal genes, example of imprinting disorder.
Chromosomal abnormalities can also occur in cancerous cells of an otherwise genetically normal individual; one well-documented example is the Philadelphia chromosome, a translocation mutation commonly associated with chronic myelogenous leukemia and less often with acute lymphoblastic leukemia.
Acquired by heredity. Sex linked or autosomal. or cancer or radiation.