The frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes was explained by

There are three genes $a,\,b,\,c$. Percentage of crossing over between $a$ and $b$ is $20\%$, $b$ and $c$ is $28\%$ and $a$ and $c$ is $8\%$. What is the sequence of genes on chromosome ?

The map distance between genes $A$ and $B$ is $3$ units, between $B$ and $C$ $10$ units and between $C$ and $A$ $7$ units. The order of the genes in a linkage map constructed on the above data would perhaps be

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? 

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