Please have a look at these useful PDF attachments for insight.

Simple and general answers :   1) inbreeding avoidance.   2) mating opportunities.  In species where a single male (or two) may dominate local mating opportunities, the only option for a young male is to leave.  In other species, the same can be true for females. 

Thank you again, Mr. Singh! Thank you also, Mr. Greenfield! 

Dear Louise

Please, read the following reference, I hope will be useful for you.

Stenseth N. C. and W. Z. Lidicker. 1992. Animal dispersal: small mammals as a model.

available at:

https://books.google.iq/books?id=7HfrCAAAQBAJ&pg=PA38&lpg=PA38&dq=genetic+reason+for+the+dispersal+of+animals&source=bl&ots=KUZiRya0TI&sig=TArsfRTdFzdHNfZOCj88CdR2Src&hl=en&sa=X&ved=0ahUKEwjCpt6ZnfrTAhWH8ywKHSKKB3oQ6AEIVzAJ#v=onepage&q=genetic%20reason%20for%20the%20dispersal%20of%20animals&f=false

Good Luck

Thank you, Mr, Hassan!