1. Male genitalia contains reproductive cells. Germ cells develop into primary spermatocytes. Each primary spermatocyte divides by the process of meiosis to form secondary spermatocytes. Secondary spermatocytes divide by the process of meiosis to form spermatids. Spermatids develop into spermatozoa. Human sperm nucleus contains 23 chromosomes. Sperm are haploid cells and carry paternal characteristics.
2. Female genitalia contain reproductive cells. Germ cells develop into primary oocytes. Each primary oocyte divides by the process of meiosis to form secondary oocytes. Secondary oocytes divide by meiosis to form oocytes. Each oocyte develops into an ovule. Human egg nucleus contains 23 chromosomes. Ovum is a haploid cell and carries the characteristics of the mother.
3. Fertilization involves the union of sperm and egg. After fertilization, the nucleus of the sperm and egg swells to form the pronucleus. The pronuclei fuse to form the zygote. A mixture of parental characteristics occurs in the zygote. It is through the zygote that the characteristics of the parents are transferred to the offspring.
4. The zygote divides repeatedly to form an embryo. A new generation is created from the embryo. In the new generation there is an assemblage of the characteristics of the parents. Thus the characteristics of the parents are transferred to the offspring.