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Q.
In individual suffering from phenylketonuria,
Principles of Inheritance and Variation
Solution:
During phenylketonuria the affected individual lacks
an enzyme that converts amino acid, phenylalanine into
tyrosine (i.e. phenylalanine hydroxylase is absent). As a
result of this phenylalanine is accumulated and
converted into phenylpyruvic acid and other derivatives.
This lack of the enzyme is due to the presence of
autosomal defective gene on chromosome number $12$.