Linkage was first observed in

$A$ genetic map is one that........

Morgan hybridized yellow-bodied,white-eyed females to brown-bodied,red-eyed males and intercrossed their $F_{1}$ progeny. He observed that:
$(a)$ $F_{2}$ ratio deviated significantly from the $9 : 3 : 3 : 1$ ratio.
$(b)$ Both genes did not segregate independently of each other.
$(c)$ Recombinant types are not obtained in $F_{2}$ generation.
$(d)$ Both genes segregate independently of each other.
Select the correct set of statements:

What is the arrangement of genes on chromosomes resulting from crossing over called?

In female $Drosophila$,linked genes show recombination during meiosis. However,such recombination does not occur during sperm formation in male $Drosophila$. Why?

Which of the following represents the frequency of recombination between two genes that are inversely proportional to the strength of linkage?