Match the columns:

Column $I$	Column $II$
$(1)$ Albinism	$(q)$ Recessive gene represented by $cc$
$(2)$ Phenylketonuria	$(s)$ Recessive gene represented by $pp$
$(3)$ Sickle cell anaemia	$(p)$ Recessive gene represented by $Hb^sHb^s$
$(4)$ Alkaptonuria	$(r)$ Recessive gene represented by $aa$

(A) The correct matches are:
$(1)$ Albinism is an autosomal recessive disorder caused by the absence of the enzyme tyrosinase,often represented by the genotype $cc$.
$(2)$ Phenylketonuria $(PKU)$ is an inborn error of metabolism caused by a recessive gene,often represented by $pp$.
$(3)$ Sickle cell anaemia is an autosomal recessive disorder caused by a mutation in the $\beta$-globin chain,represented by the genotype $Hb^sHb^s$.
$(4)$ Alkaptonuria is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme homogentisate $1,2-$dioxygenase,often represented by the genotype $aa$.
Therefore,the correct matching is $(1-q), (2-s), (3-p), (4-r)$.