Klinefelter's Syndrome is a genetic disorder that also caused due to the presence of an additional copy of X chromosome resulting into a karyotype of 47 , XXY. Such an individual has overall masculine development, however, the feminine development (development of breast, i.e., Gynaecomastia) is also expressed. Such individuals are sterile. Down syndrome was first described by Langdon down (1866). In this disorder affected individual is physically, psychomotorly and mentally retarded.

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