Since the nucleus replicates , that is, makes an exact copy of itself, it must therefore duplicate the information, and the new individuals so produced must be identical. This form of reproduction allows for no variation . The obvious advantage of asexual reproduction is that it requires no mating, no transfer of sex cells and so on. Making sure that there is no variation is a good thing too, providing that the habitat does not change. Amoeba have happily occupied their niche in stagnant water everywhere for millions of years.
Higher plants make use of asexual reproduction as well.
None of these need seeds to produce the next year's growth. In sexual reproduction , two individuals are needed - a male and a female . The two sexes make special cells - the gametes have a selection of chromosomes, and therefore information, from the parents. When these are brought together, in fertilization , the cell which is produced will have some characteristics from each of the parent individuals. Flies may all look alike to you, but if you look closely enough, you'll find hundreds of differences.