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Trisomy 21. Down syndrome (also known by the karyotype 47,XX,+21 for females and 47,XY,+21 for males) [98] is mostly caused by a failure of the 21st chromosome to separate during egg or sperm development, known as nondisjunction. [91] As a result, a sperm or egg cell is produced with an extra copy of chromosome 21; this cell thus has 24 ...
An epicanthic fold or epicanthus[6] is a skin fold of the upper eyelid that covers the inner corner (medial canthus) of the eye. [3] However, variation occurs in the nature of this feature and the possession of "partial epicanthic folds" or "slight epicanthic folds" is noted in the relevant literature. [7][8][9] Various factors influence ...
Waardenburg syndrome is a group of rare genetic conditions characterised by at least some degree of congenital hearing loss and pigmentation deficiencies, which can include bright blue eyes (or one blue eye and one brown eye), a white forelock or patches of light skin. These basic features constitute type 2 of the condition; in type 1, there is ...
Human cells typically contain 23 pairs of chromosomes — one from the mother and one from the father in each pair. When there is an extra chromosome 21, the result is Down syndrome ...
Piebaldism. Piebaldism refers to the absence of mature melanin-forming cells (melanocytes) in certain areas of the skin and hair. It is a rare autosomal dominant disorder of melanocyte development. [2]: 867 Common characteristics include a congenital white forelock, scattered normal pigmented and hypopigmented macules and a triangular shaped ...
In honor of Down Syndrome Awareness Month, which happens every October, we rounded up some informative facts about the chromosomal condition.
Medical genetics. Noonan syndrome with multiple lentigines (NSML) which is part of a group called Ras / MAPK pathway syndromes, [2] is a rare autosomal dominant, [3] multisystem disease caused by a mutation in the protein tyrosine phosphatase, non-receptor type 11 gene (PTPN11). The disease is a complex of features, mostly involving the skin ...
Genetics of Down syndrome. Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on chromosome 21, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies greatly from individual to individual, depending on the extent of the extra copy ...