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

Which one of the following statements is $NOT$ true regarding crossing over during meiosis?

When two genes are situated very close to each other in a chromosome,

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

The first attempt to demonstrate linkage in plants was made in $.....$.

What was the phenotypic ratio obtained in the experiment on linkage and recombination performed in Lathyrus odoratus (Sweet Pea)?