Although modified to perform a different task, a horse's front leg is made up of the same bones as is your arm. this suggests a common ancestor between horses and humans that also had those bones in its forelimb. the horse leg and human arm are therefore considered to be structures.

I believe the horse leg and human arm are therefore considered to be Homologous structures. 
Homologous structures are structures with similar ancestries and common traits, however; they have different functions. For example the horse leg and human arm have similar origin but have different functions. On the other hand; analogous structures have different evolutionary ancestries but they have the same functions. Examples of these are the wings of birds, bats and insects. 

They create genetic variations

The answer is reflection.