Who put forward the “Theory of linkage''

Crossing over causes

Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in $\mathrm{F}_{2}$ generation for a dihybrid cross?

Frequency of crossing over in a chromosome is an index of

Genes $A, B$ and $C$ are linked. Genes $A$ and $B$ are more close 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 crosses has occurred between $A$ and $C$ than $A$ and $B$