The major genetic differences lies in the difference in sex chromosome of sperm( male gamete) and egg( female gamete). Sperm has Y chromosome as sex chromosome, while egg has X chromosome as sex chromosome. There is a marked difference in size, shape , metabolic activity , cytoplasm content, motility, etc in the sperms and eggs.
Human eggs are much larger than sperms and are highly metabolically active cells. They contain more amount of cytoplasm.