With this overview of anatomy in mind (a)   , we turn to , which is the production of gametes.

(a)   , the formation and development of sperms , is continuous and prolific in adult human males.

Non-motile (a)   undergo a process called differentiation, to become motile, streamlined sperm.

During fetal development, (a)   undergo mitosis thousands of times until their number reach 2 million of more

Meoisis is completed by a primary (a)   each month in response to the LH surge

Oogenesis, the development of mature oocytes (eggs), is a prolonged process in the human female

(a)  

The mammary glands are present in both sexes, but they normally produce milk only in females

(a)  

(a)   occurs throughout adolescence and adulthood. In contrast, the mitotic divisions that occur in oogenesis in human females are thought to be complete before birth, and the production of mature gametes ceases at about age 50. •

Spermatogenesis produces mature sperm from precursor cells in a continuous sequence, whereas there are long interruptions in (a)  

The stem cells arise from division and differentiation of primordial germ cells in the embryonic testes. In mature testes, they divide mitotically to form (a)   , which in turn generate spermatocytes by mitosis

The structure of a sperm cell fits its function. In humans, as in most species, a head containing the haploid nucleus is tipped with a special vesicle, the (a)   , which contains enzymes that help the sperm penetrate an egg. Behind the head, many mitochondria (or one large mitochondrion in some species) provide ATP for movement of the flagellar tail.

Oogenesis begins in the female embryo with the production of (a)   from primordial germ cells.

The oogonia divide by mitosis to form cells that begin meiosis, but stop the process at prophase I before birth. These developmentally arrested cells, which are primary (a)   , each reside within a small follicle, a cavity lined with protective cells. At birth, the ovaries together contain about 1–2 million primary oocytes, of which about 500 fully mature between puberty and menopause.

Beginning at puberty, follicle-stimulating hormone (FSH) periodically stimulates a small group of follicles to resume growth and development. Typically, only one follicle fully matures each month, with its (a)   completing meiosis I . The second meiotic division begins, but stops at metaphase.

Arrested in meiosis II, the (a)   is released at ovulation, when its follicle breaks open. Only if a sperm penetrates the oocyte does meiosis II resume.