Klinefelter's syndrome or XXY syndrome is a disorder in males where affected individuals have a pair of X chromosomes instead of just one, and is associated with additional risk for some medical conditions. It is named after Dr. Harry Klinefelter, a medical researcher at Massachusetts General Hospital who first described this condition in 1942.

    The XXY chromosomal rearrangement is one of the most common, occurring in 1 in 500 live births. Other rearrangements, though less common, can also result in the phenotypic characteristics of this disorder. In mammals with more than one X chromosome, the genes on all but one X chromosome are barred from being expressed. This happens in XXY males as well as XX females. A few genes, however, have corresponding genes on the Y chromosome and are not barred. These triploid genes in XXY males may be responsible for symptoms associated with Klinefelter's syndrome.

    Klinefelter’s syndrome is irreversible, but many of the symptoms can be managed with testosterone therapy. Afflicted individuals are sterile, and some may exhibit a significant degree of feminization. As with the XY male population, there is considerable variation among XXY individuals. Therefore, diagnosis cannot be made on body type alone. Karyotype is the gold standard for diagnosis.
Figure 1. Karyotype of XXY Male


Question #00010

According to the information in the passage, the mode of inheritance of Klinefelter’s syndrome in humans is:

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