If the gene exchange rate (recombination frequency) of two linked genes is $30\%$,then the distance between these two genes is:

Genes $A, B$,and $C$ are linked. Genes $A$ and $B$ are closer than $A$ and $C$. Find out the correct option for the given statements:
$I.$ $A$ might be before $B$ and $C$
$II.$ $B$ might be between $A$ and $C$
$III.$ $C$ might be between $A$ and $B$
$IV.$ More crossovers have occurred between $A$ and $C$ than $A$ and $B$.

Two dominant non-allelic genes are $50$ map units apart. The linkage present is:

Crossing over causes

Give scientific reasons: Linkage and crossing over of genes are alternatives of each other.

Genetic variation is observed in sexually reproducing species.