What is the reason for the absence of hybrids?

What is a genetic map?

In maize, colored endosperm $(C)$ is dominant over colorless $(c)$ and full endosperm $(R)$ is dominant over shrunken $(r)$. When a test cross is performed on the $F_1$ generation, the following results are obtained:
Colored and Full = $45\%$
Colored and Shrunken = $5\%$
Colorless and Full = $4\%$
Colorless and Shrunken = $46\%$
Based on this data, what is the distance between the two non-allelic genes (in $units$)?

Which of the following animals was selected by $T.H. Morgan$ for studying linkage?

In the fruit fly $Drosophila$,the lack of independent assortment between genes $A$ and $B$ is due to .....

Why did Morgan work with the fruit flies $(Drosophila \text{ } melanogaster)$?