Genes which are located on the same chromosome are

For the preparation of genetic maps,the recombination frequencies between genes are additive over short distances but not over long distances due to

. . . . . . $(B)$ . . . . . . 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.
$(A) \quad\quad (B)$

Linkage in $Drosophila$ was discovered by:

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:

Crossing over in a diploid organism is responsible for