As the length of the chromosome increases in an organism,which of the following increases?

Genetic maps of chromosomes are based on the frequency of $:-$

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?

The presence of recombinants is due to.....

Linked genes are present on

$A$ : In block inheritance of all genes located on the same chromosome may occur in some organisms.
$R$ : Dihybrid test cross will have only two phenotypes.