Phenylketonuria is a genetic disorder due to a defect in the metabolism of which of the following?

Which autosome-linked disease is related to the following pedigree analysis?

$A$: The heterozygotic female for haemophilia may transmit the disease to sons.
$R$: Such traits show criss-cross inheritance.

$A$ haemophilic female marries a normal male. What will be the theoretical ratio of their offspring regarding haemophilia?

Pick out the correct statements.
$(1)$ Haemophilia is a sex-linked recessive disease.
$(2)$ Down's syndrome is due to aneuploidy.
$(3)$ Phenylketonuria is an autosomal recessive gene disorder.
$(4)$ Sickle cell anaemia is an $X$-linked recessive gene disorder.

Which of the following is not a correct statement regarding Phenylketonuria?