Which is the most common mechanism of genetic variation in the population of a sexually reproducing organism?

What is the name of the pea species used by Bateson and Punnett in their experiments?

Who clearly proved and defined linkage?

. . . . . . $(B)$ . . . . . . used the frequency of recombination between gene pairs on the . . . . . . $(A)$ . . . . . . as a measure of the distance between genes and mapped their position on the chromosome.
$(A) \quad\quad (B)$

$A$: Morgan's cross $III$ was conducted in $Drosophila$ to locate genes on the chromosome for white eye color.
$R$: The cross was done between red-eyed hybrid female and white-eyed male.

When white-eyed and miniature-winged $Drosophila$ $melanogaster$ is crossed with its wild type,it produces which of the following percentages of recombinants (in $\%$)?