Sex linked genetic disorders
Fragile x syndrome
Sex-linked traits are genetic characteristics determined by genes located on sex chromosomes. Genes are pieces of DNA on chromosomes that carry information that are responsible for inheriting traits. Different forms of the same gene are called alleles. One allele for a certain trait is inherited from a mother and one from a father. These traits are passed down from parent to their offspring by sexual reproduction. Fragile X syndrome (FXS) or Martin-Bell syndrome is a genetic syndrome that causes autism and mental retardation among boys. Some symptoms of FXS are severe intellectual disabilities as well as physical symptoms such as a larger than usual face, large ears, large testicles and behavioral characteristics such as stereotypic movements and social anxiety. Fragile X syndrome is associated with the CGG trinucleotide expanding affecting the fragile X mental retardation 1 gene on the X chromosome, resulting in a failure to express the fragile X mental retardation protein which is required for normal neural development. Depending on the length of the CGG repeat, an allele may be classified as normal (unaffected by the syndrome), a premutation (at risk of fragile X associated disorders), or full mutation (usually affected by the syndrome). Fragile X syndrome has traditionally been considered an X-linked dominant condition with variable expressivity and possibly reduced penetrance. However, due to genetic anticipation and X-inactivation in females, the inheritance of Fragile X syndrome does not follow the usual pattern of X-linked dominant inheritance and some scholars have suggested discontinuing labeling X-linked disorders as dominant or recessive. The X chromosome information is expressed than the Y chromosome so whatever X chromosome is passed to the male offspring it will be expressed in the male. Rarely is it ever expressed in female offspring because that chromosome with sex-trait is less dominant than...
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