Question

What is point mutation? Give one example.

Answer 1

When heritable changes occur in a very short region of the DNA molecule, such as a single nucleotide or nucleotide pair, these are referred to as point mutations. Point mutations can be caused by inversion, substitution (transition and transversion), or frameshift (insertion and deletion) nucleotide changes in DNA or RNA. Phenylketonuria (PKU; Polling 1934) is an inborn, autosomal, recessive metabolic condition in which the homozygous recessive individual lacks the enzyme phenylalanine hydroxylase, which is required to convert phenylalanine (amino acid) to tyrosine (amino acid) in the liver. It causes hyperphenylalaninemia, which is marked by the accumulation and excretion of phenylalanine, phenylpyruvic acid, and other substances. The enzyme lack is caused by a defective autosomal recessive gene on chromosome 12. This gene is faulty as a result of replacement. Affected child are OK at birth, but within a few weeks, plasma phenylalanine levels spike (30-50 times), impairing brain development. Other signs include mental impairment, reduced pigmentation in the hair and skin, and eczema.