question_answer

Which of the following is not an autosomal recessive trait?

A)                  Phenylketonuria                            

B)  Cystic fibrosis

C)                  Albinism                                             

D)  Polydactyly

Correct Answer: D

Solution :

                 Polydactyly means extra digit is caused by dominant gene. One parent carries the defective gene and may the children inherit it. Phenylketonuria is autosomal recessive disorder. This metabolic error is due to deficiency of an enzyme phenylalanine hydroxylase, which converts phenylalanine into tyrosine. The excess of phenylalanine is converted into pyruvic acid. This is characterised by mental retardation, seizures and a typical odour of skin and urine. Phenylalanine \[\xrightarrow{{}}\] Phenyl Pyruvic acid p-hydroxy Phenyl Pyruvic acid \[\xleftarrow[ketonuria]{Phenyl}\] Cystic fibrosis is autosomal recessive disorder. It occurs when an individual is homozygous for allele that encodes a defective version of the protein regulating the chloride transport channel. It is characterised by mucus, clogging lungs, liver and pancreas. Albinism is also autosomal recessive disorder, which is due to absence of melanin pigment and individuals suffering from this disease are incapable of converting dihydroxy phenyl alanine into melanin.