The amino acid substituted in sickle cell anaemia is

In Huntington's disease,the unaffected persons are homozygous for normal allele $h$. The following pedigree is erroneous because:

The gene for haemophilia is located on the $X$ chromosome. Hence,it is normally impossible for a:

With the help of the given pedigree,find out the probability for the birth of a child having no disease and being a carrier (has the disease mutation in one allele of the gene) in the $F_3$ generation.

Match the columns:

Column $I$	Column $II$
$(a)$ Sickle cell anaemia	$(x)$ Homogentisic acid
$(b)$ Alkaptonuria	$(y)$ Melanin pigments are absent
$(c)$ Albinism	$(z)$ More amount of phenylalanine
$(d)$ Phenylketonuria	$(w)$ Defective haemoglobin

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.