In the following human pedigree, the filled symbols represent affected individuals. Mark the correct statement with regard to the pedigree chart.

The trait is observed in a male and female offspring of $4^{\mathrm{th}}$ generation. Neither of the parents exhibit the trait. Hence is it recessive. Also, no criss cross inheritance is observed, so it is autosomal. PKU is a autosomal recessive disorder.

Colourblindness and haemophilia are sex-linked recessive disorders.