What is pedigree analysis? Suggest how such an analysis, can be useful.

Sickle cell-anaemia disorder arises due to

Pick out the correct statements.

$I.$ Haemophilia is a sex-linked recessive disease

$II.$ Down's syndrome is due to aneuploidy

$III.$ Phenylketonuria is an autosomal dominant gene disorder

$IV.$ Phenylketonuria is an autosomal recessive gene disorder

$V.$ Sickle cell anaemia is an $X$-linked recessive gene disorder

Among symbol $A, B$ and $C, C$ indicates