Why gamete has half/twice the number of chromosomes that a body cells has?

Dear Student, 

Gametes are produced as a result of meiosis which is reductional division. When two gametes belonging to opposite sexes combine then the chromosome number is restored back. Thus halving of the chromosome number in gametes maintains the chromosome number of a species. So, gametes have half the number of chromosomes than the other body body cells. 

Regards