Which scientists proposed the coupling and repulsion theory?

Who put forward the "Theory of linkage"?

Thomas Hunt Morgan and his colleagues performed experiments on which organism to verify the chromosomal theory of inheritance and later demonstrated linkage?

The scientists who proposed the theory of linkage are

$A$ cross is made between two homozygous individuals, one with the wild type $(+, +)$ and the other with the mutant type $(a, b)$. In the $F_2$ generation (or test cross progeny), out of $1000$ individuals, $700$ are parental types. Calculate the distance between genes $a$ and $b$.

The theory of recombination of linked genes due to crossing over of chromosomes during the pachytene stage of meiosis was put forward by: