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  4. Which of the following is mismatched pair of disease and its related symptom ? Disease Symptom (a) Phenylketonuria Urine turns black on exposure to air (b) Down's syndrome Physical and mental retardation (c) Klinefelter's syndrome Sterile males (d) Turner's syndrome Sterile females

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Q. Which of the following is mismatched pair of disease and its related symptom ?
Disease Symptom
(a)$\,\,$ Phenylketonuria$\,\,$ Urine turns black on exposure to air
(b)$\,\,$ Down's syndrome$\,\,$ Physical and mental retardation
(c)$\,\,$ Klinefelter's syndrome$\,\,$ Sterile males
(d)$\,\,$ Turner's syndrome$\,\,$ Sterile females

Principles of Inheritance and Variation

Solution:

Phenylketonuria is an inherited error of metabolism caused by the deficiency of enzyme phenylalanine hydroxylase. This enzyme is required for the conversion of phenylalanine into tyrosine. Thus, deficiency of this enzyme leads to over production of phenylalanine and its conversion to phenyl pyruvic acid and other derivatives, which accumulate in cerebrospinal fluid leading to severe mental retardation, and also get excreted in urine due to poor absorption by kidney. This disease is inherited as an autosomal recessive trait. Alkaptonuria is the disease in which urine turns black on exposure to air.