Q.Write a note on PKU (phenylketonuria).

Human somatic cells carry 23 pairs of chromosomes: one pair of sex chromosomes plus 22 pairs of autosomes, which govern the great majority of traits unrelated to sex. Autosomal inheritance is the transmission of these traits from parent to offspring through the autosomes; unlike sex-linked traits, autosomal traits appear with equal frequency in males and females.

Autosomal dominant traits appear in both homozygous dominant and heterozygous individuals — widow's peak (a V-shaped hairline) is the textbook example, appearing in $WW$ and $Ww$ genotypes, with only the homozygous recessive ($ww$) genotype giving a straight hairline. Autosomal recessive traits, by contrast, appear only in homozygous recessive individuals and tend to skip generations, hiding in unaffected heterozygous carriers — phenylketonuria (PKU) is the textbook example, an inborn meta …