$A$ - Sickle-cell anaemia is a sex-linked recessive trait.
$R$ - This disease is controlled by more than two pairs of alleles.

$A$ husband and wife have normal vision,but the fathers of both of them were colour blind. What is the probability of their first daughter being colour blind (in $\%$)?

Mr. Stevan is suffering from haemophilia and cystic fibrosis. His father is heterozygous for cystic fibrosis. The probability of Stevan's sperm having recessive $X$-linked as well as autosomal allele is

Select the correct options for the given statements:
Statements:
$X$: Formation of Haemoglobin is controlled by two closely linked genes $HBA1$ and $HBA2$ on chromosome $16$ of each parent.
$Y$: $\beta$-Thalassemia is controlled by a single gene $HBB$ on chromosome $21$ of each parent.

Polydactyly in humans is due to:

Which disorder is caused when the synthesis of the $\beta$-globin chain of hemoglobin is affected due to a single gene $HBB$,leading to a quantitative change in the hemoglobin structure?