Asexual reproduction is a form of reproduction that does not involve fusion of gametes (egg and sperm cells), producing offspring that are genetically identical to the parent. It is often a quick process. Various organisms use different forms of asexual reproduction. For example, flatworms undergo a process called fragmentation in which they divide in two, then each half regenerates into a new flatworm. Each regenerated form is identical to the original. Parthenogenesis is a form of asexual reproduction in which an unfertilized egg cell becomes a new organism. It has been described in a small number of species of bees, parasitic wasps, fish, and lizards.
Sexual reproduction is a form of reproduction involving fusion of gametes, producing genetically unique offspring. It requires the fertilization of an egg cell by a sperm to generate a zygote. This zygote eventually becomes an embryo once it has undergone several rounds of cell division and development. In mammals, when the embryo has developed further, it is called a fetus. Sexual reproduction results in offspring with a mix of genetic information from the two parents.In mammals, the reproductive system is more complex, and there are more organs involved in the production of offspring. Gametes are produced in the testes in males and ovaries in females. In males, the testes produce sperm, which are contained in a fluid called semen. Semen and additional secretions are released from accessory glands such as the seminal vesicles, prostate gland, and bulbourethral gland. The sperm travel through the vas deferens before being released through the penis, which is external to the body. In females, ovaries are the site of egg development. After an egg is released during ovulation, it travels down a fallopian tube or oviduct before it enters the uterus. Fertilization occurs in the fallopian tube, but the developing embryo develops in the uterus.