Drosophila has four pairs of chromosomes. How many linkage groups does it have?

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

$A$ genetic map is one that........

When a group of genes exhibits linkage,they:

The linkage map of a fruit fly has a total map distance of $66$ units. The gene for yellow body $(a)$ is at one end and the gene for short hair $(y)$ is at the other end. What will be the recombination frequency between these two genes $(a$ and $y)$?

The term "linkage" was coined by