Who used the frequency of recombination as a measure of the distance between genes on a chromosome and mapped their position?

Genetic variation is observed in sexually reproducing species.

The linkage map of a fruit fly has a total map distance of $66$ units. The gene for yellow body $(a)$ is at one end and the gene for short hair $(y)$ is at the other end. What will be the recombination frequency between these two genes $(a$ and $y)$?

The arrangement of genes on chromosomes is

Genes on the same chromosome can be:

When closely placed genes on the same chromosome are inherited together,the phenomenon is known as: