Exchange of genetic material between chromatids of homologous chromosomes during meiosis is called

Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their $F_{1}$ progeny. He observed that

$(a)$ $F_{2}$ ratio was deviated very 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 :

The recombination frequency between the genes $a\, \& \, c$ is $5 \,\% \,, b\, \& \,c$ is $15 \,\%,\, b\, \& \,d$ is $9 \%, \,a\, \& \,b$ is $20 \%$ , $c\, \& \,d$ is $24 \%$ and $a \, \& \,d$ is $29 \%$. What will be the sequence of these genes on a linear chromosome? 

Describe linkage and recombination in detail.
 

$A$ : Morgan's cross III was conducted in Drosophila to locate genes on chromosome for white eye colour.
$R$ : The cross was done between red eyed hybrid female and white eyed male.

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