Genes which are located on the same chromosome are

When a test cross is performed between $F_1$ hybrid flies,the parental type offspring are produced in much higher frequency than the recombinant type offspring. What does this indicate?

What is the result of linkage and crossing over?

$A$ cross is made between two homozygous individuals, one with the wild type $(+, +)$ and the other with the mutant type $(a, b)$. In the $F_2$ generation (or test cross progeny), out of $1000$ individuals, $700$ are parental types. Calculate the distance between genes $a$ and $b$.

Give differences: Crossing over and Linkage.

Frequency of crossing over in a chromosome is an index of