In Mendelism, linkage was not observed due to

$A$ : Crossing over is exchange of genetic material between non-homologous chromosomes.
$R$ : It produces new linkages.

Frequency of crossing over in a chromosome is an index of

Mendel observed that some characters did not assort independently. Later researchers found it to be due to

In order to calculate map distance of genes on a chromosome, one must know the

The term “linkage” was coined by