Concept 32.1 Reproduction Can Be Sexual or Asexual

• Asexual reproduction produces offspring that are genetically identical to their parent and to one another; it produces no genetic diversity.
   
• Modes of asexual reproduction include budding, regeneration, and parthenogenesis. Review Figure 32.1
   
• Sexual reproduction consists of three basic steps: gametogenesis, spawning or mating, and fertilization.
   

Concept 32.2 Gametogenesis Produces Haploid Gametes

• Gametogenesis occurs in testes and ovaries. In spermatogenesis (the production of sperm) and oogenesis (the production of ova), the germ cells proliferate mitotically, undergo meiosis, and mature into gametes. Review Figure 32.2
   
• Each primary spermatocyte produces four haploid sperm through the two cell divisions of meiosis.
   
• Primary oocytes immediately enter prophase of the first meiotic division, and in many species, including humans, their development is arrested at this point. Each primary oocyte produces only one ovum.
   
• In hermaphroditic species, the same individual can produce both sperm and ova, either simultaneously or sequentially.
   

Concept 32.3 Fertilization Is the Union of Sperm and Ovum

• External fertilization is common in aquatic species. Spawning is the release of large numbers of gametes into the water.
   
• Internal fertilization is necessary in terrestrial species. It usually requires copulation, the physical joining of the male and female accessory sex organs.
   
• Fertilization involves species-specific binding of sperm to ovum, the acrosomal reaction, the sperm's passage through the protective layers covering the ovum, and fusion of sperm and ovum plasma membranes. Review Figure 32.3 and ANIMATED TUTORIAL 32.1
   
• The entry of the sperm into the ovum triggers blocks to polyspermy, which prevent additional sperm from entering the ovum, and in mammals, signal the ovum to complete meiosis.
   

Concept 32.4 Human Reproduction Is Hormonally Controlled

• The male sex organs produce and deliver semen. Semen consists of sperm suspended in seminal fluid, which nourishes the sperm and facilitates fertilization. Review Figure 32.5 and WEB ACTIVITY 32.1
   
• Sperm are produced in the seminiferous tubules of the testes, mature in the epididymis, and are delivered to the urethra through the vasa deferentia. Review Figure 32.6 and WEB ACTIVITY 32.2
   
• Spermatogenesis depends on testosterone secreted by the Leydig cells of the testes, which are under the control of hormones produced in the anterior pituitary and hypothalamus. Review Figure 32.7
   
• Ova mature in the female's ovaries and are released into the oviducts. Sperm deposited in the vagina during copulation move up through the cervix and uterus into the oviducts, where fertilization occurs. Review Figure 32.8 and WEB ACTIVITY 32.3
   
• The maturation and release of ova constitute an ovarian cycle. This cycle takes about 28 days. The uterine cycle prepares the endometrium of the uterus for receipt of an embryo. If no embryo arrives, the endometrium sloughs off in the process of menstruation. Review Figures 32.9 and 32.10 and ANIMATED TUTORIAL 32.2
   
• Both the ovarian and the uterine cycles are under the control of hypothalamic and pituitary hormones, which in turn are under the feedback control of estrogen and other hormones. Review Figure 32.11
   

Concept 32.5 Humans Use a Variety of Methods to Control Fertility

• Methods of contraception include abstention from intercourse and the use of technologies that decrease the probability of fertilization and implantation. Review Table 32.1
   
• A number of assisted reproductive technologies (ARTs) have been developed to treat infertility.