Which scientist explained linkage and recombination in Drosophila?

Geneticists plot the relative locations of genes on chromosomes by which of these methods?

Two genes $R$ and $Y$ are located very close on the chromosomal linkage map of maize plant. When $RRYY$ and $rryy$ genotypes are hybridized,then $F_{2}$-segregation will show

Linkage in $Drosophila$ was discovered by:

The number of linkage groups in $E. coli$ is:

The recombination frequency between the genes $a$ and $c$ is $5\%$,$b$ and $c$ is $15\%$,$b$ and $d$ is $9\%$,$a$ and $b$ is $20\%$,$c$ and $d$ is $24\%$,and $a$ and $d$ is $29\%$. What will be the sequence of these genes on a linear chromosome?