Answer: Two species with different number of chromosomes can interbreed but chances of getting fertile offspring is low. Example horses have 32 pair of sex chromosomes and in donkey there are 31 pair of sex chromosomes. The resultant hybrid is mule which remains sterile because of the presence of one extra chromosome poses a problem when comes in distribution of sex chromosomes. This hybrid will not be able to interbreed with either of it's parents. This is not common in nature as two different species only interbred when they find common sexual similarity.
