This is another chromosome abnormality. Kleinfelter’s syndrome is due to the abnormality of sex chromosomes.
Individuals exhibit abnormality only during adulthood, childhood being normal. Affected individuals are males. The symptoms are-
(i) Absence of spermatogenesis
(ii) Excessive secretion of gonodotropins in the urine
(iii) Genitalia underdeveloped
(iv) Sparse body hair
(v) Some degree of breast development
(vi) Mental retardation
(vii) Effeminate behavior
Cytological study of these individuals shows that they are basically males, but have an extra X chromosome- they are XXY. They have a total of 47 chromosomes instead of 46. This abnormality occurs during meiosis due to the non separation of the two X chromosomes. As a result, some eggs will have 2X chromosomes instead of one. If such an egg (22 autosomes + 2X
chromosomes) is fertilized by a normal sperm (22+Y) the resultant individual will be a Kleinfelter’s Syndrome.