Which of the following statements are incorrect? $(i)$ $ABO$ blood grouping is controlled by gene $I$. (ii) Gene $I$ has four alleles. (iii) $I^A$ and $I^B$ produce the same type of sugar. (iv) $I$ or $i$ produces a different type of sugar. $(v)$ $I^A$ and $I^B$ are incompletely dominant.

$A$ hereditary disease,which is never passed on from father to son,is:

Which of the following statements are false?
$I.$ $A$ dominant allele determines the phenotype when paired with a recessive allele.
$II.$ $A$ recessive allele is weaker than a dominant allele.
$III.$ $A$ recessive allele does not show its effects when paired with a dominant allele.
$IV.$ $A$ dominant allele is always better for an organism.

The phenotype of an individual may be affected if the modified allele produces:
$(a)$ No enzyme at all
$(b)$ The normal/less efficient enzyme
$(c)$ $A$ non-functional enzyme

Assertion $A$: Gene is the unit of inheritance.
Reason $R$: The properties of tissues are due to the constituents of their cells.
Which option is correct for Assertion $A$ and Reason $R$?

The $F_2$ dihybrid ratio $9 : 3 : 4$ is explained on the basis of