Sexual reproduction involves both haploid and diploid cells. (A) Cells in higher eucaryotic organisms proliferate in the diploid phase to form a multicellular organism; only the gametes (the egg and the sperm) are haploid. (B) These gametes reunite at fertilization to generate a diploid zygote, which will develop into a diploid organism. For simplicity, only one chromosome is shown for each gamete, and the sperm cell has been greatly enlarged.  Fair Use and Copyright info