Crossing over in a diploid organism is responsible for

Continuous variations are attributed to

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 a linkage group?

The lack of independent assortment of two genes $A$ and $B$ in the fruit fly $Drosophila$ is due to:

In $Drosophila$,crossing over occurs in females but not in males. Genes $A$ and $B$ are located on a chromosome at a distance of $10 \ cM$. The genotype of the female $Drosophila$ is $AB/ab$ and the genotype of the male $Drosophila$ is $AB/ab$. How many types of gametes are produced by the female and male $Drosophila$,respectively?