The offspring from a cross between two individuals differing in at least one set of characters is called

In sickle cell anaemia$-$

Identify the correct statement.

Match the following columns correctly:

Column-$I$	Column-$II$
$(a)$ $1 : 2 : 1$	$(i)$ Test cross
$(b)$ $3 : 1$	$(ii)$ Law of Dominance
$(c)$ $9 : 3 : 3 : 1$	$(iii)$ Incomplete Dominance
$(d)$ $1 : 1 : 1 : 1$	$(iv)$ Law of Independent Assortment
	$(v)$ Law of Segregation

Based on the statements, choose the correct option given below.
Statement-$I$: Allelic genes lead to individual differences within the species.
Statement-$II$: About $1000$ varieties of mangoes are found in India.

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 $R$?