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Turner syndrome (TS), commonly known as 45,X, or 45,X0, [note 1] is a chromosomal disorder in which female cells have only one X chromosome instead of two, or are partially missing an X chromosome (sex chromosome monosomy) leading to the complete or partial deletion of the pseudoautosomal regions (PAR1, PAR2) in the affected X chromosome.
Location of the FMR1 gene on the X chromosome. Fragile X syndrome is a genetic disorder which occurs as a result of a mutation of the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene on the X chromosome, most commonly an increase in the number of CGG trinucleotide repeats in the 5' untranslated region of FMR1.
This means that males affected by an X-linked recessive disorder inherited the responsible X chromosome from their mothers. Second, X-linked recessive traits are more commonly expressed in males than females. [2] This is due to the fact that males possess only a single X chromosome, and therefore require only one mutated X in order to be affected.
An X-linked genetic disease is a disease inherited through a genetic defect on the X chromosome. In human cells, there is a pair of non-matching sex chromosomes , labelled X and Y. Females carry two X chromosomes, whereas males have one X and one Y chromosome .
Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome. [citation needed] An example of trisomy in humans is Down syndrome, which is a developmental disorder caused by an extra copy of chromosome 21; the disorder is therefore also called "trisomy 21". [7]
In Turner syndrome, a chromosomal abnormality in which a person exhibits X chromosome monosomy, patients are at a great risk of developing autoimmune thyroid disease since their genotype mimics an extreme form of X chromosome inactivation since there is only one X chromosome that can be expressed.
Human conditions due to monosomy: Turner syndrome – Females with Turner syndrome typically have one X chromosome instead of the usual two X chromosomes. Turner syndrome is the only full monosomy that is seen in humans — all other cases of full monosomy are lethal and the individual will not survive development.
Males with Klinefelter syndrome typically have one extra copy of the X chromosome in each cell, for a total of two X chromosomes and one Y chromosome (47,XXY). It is less common for affected males to have two or three extra X chromosomes (48,XXXY or 49,XXXXY) or extra copies of both the X and Y chromosomes (48,XXYY) in each cell.