ABSTRACT
Sex Chromosomes Defects involving sex chromosomes are interesting because the individual carrying the abnormality may be phenotypically (outwardly) either a male or a female and the sex chromosome involved may be either an X or a Y chromosome. Some males are known to have the sex chromosome make-ups XYY or XXY, the latter of which gives rise to Klinefelter's syndrome (Fig. 19-4). People with Klinefelter's syndrome have a male phenotype and small testes lacking sperm, are sterile, and are often mildly mentally retarded. Such men are often tall.
