The number of linkage groups in $Pisum \text{ } sativum$ is

Frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes to map their position on the chromosome was used for the first time by

Who performed the first experiment on linkage and recombination?

Which method can be used to determine the location of specific genes on a chromosome?

The linkage map of $X$-chromosome of fruit fly has $66$ units with yellow body gene $(y)$ at one end and bobbed hair $(b)$ gene at the other end. The recombination frequency between these two genes ($y$ and $b$) should be

What happens in the process of variation?