Gametes are produced by specialized organs called gonads: the testes in males and the ovaries in females. These organs contain precursor cells that undergo a special type of cell division called meiosis, which cuts the chromosome count in half so that when a sperm and egg combine, the resulting embryo has the correct number of chromosomes. In plants, gamete production follows a different path but serves the same purpose.
How Gonads Form in the First Place
The cells that eventually produce gametes don’t start out in the gonads. In a developing embryo, precursor cells called primordial germ cells first appear in the outer cell layer during the earliest weeks of development. They then embark on a long migration through the embryo’s tissues, traveling through the developing gut and surrounding tissue before finally reaching the gonadal ridges, the structures that will become either testes or ovaries.
This journey is guided by chemical signals. The developing gonads release a homing signal that the migrating cells detect through receptors on their surface. Along the way, surrounding tissues provide survival signals that keep the cells alive during transit. Once these precursor cells arrive and settle into the gonads, they become the foundation for all future gamete production.
Sperm Production in the Testes
The testes produce sperm inside tightly coiled structures called seminiferous tubules. Lining the walls of these tubules are stem cells that continuously divide. Through a series of mitotic divisions, each stem cell produces increasingly specialized cells that eventually enter meiosis. Meiosis I halves the chromosome count, and meiosis II splits those cells again, yielding four cells from each original precursor. These cells then undergo a final transformation, growing a tail and shedding excess material, without any additional cell division. The finished sperm are then released into the center of the tubule.
Supporting cells called Sertoli cells play a critical role throughout this process. They physically cradle developing sperm cells, supply nutrients, and respond to hormonal signals that keep production running. The entire process from stem cell to mature sperm takes roughly 64 to 72 days in humans.
Men produce sperm continuously from puberty onward. A healthy male produces tens of millions of sperm per day. In one study of 20 healthy men, a single ejaculate after a few days of abstinence contained an average of about 252 million total sperm. With daily ejaculation, that number dropped to around 106 million by the third day and then plateaued, showing that production is constant but stores need time to replenish. Unlike women, men don’t experience an abrupt end to fertility. Sperm production slows gradually with age, but some men remain fertile well into their later years.
Egg Production in the Ovaries
The ovaries take a fundamentally different approach. A female fetus begins producing egg precursor cells early in development. By the 20th week of pregnancy, a female fetus has roughly 6 to 7 million of these cells. They enter the first stage of meiosis and then pause, locked in a holding state surrounded by a single layer of nourishing cells. This unit is called a primordial follicle.
Most of these follicles degrade before birth and throughout childhood. By puberty, several hundred thousand remain. Each month after puberty, a small group of follicles begins to mature. The egg inside enlarges, the surrounding cell layer multiplies and thickens, and a fluid-filled cavity forms. Typically only one follicle completes the process each cycle. That egg finishes its first meiotic division just before ovulation, producing a cell with half the normal chromosome count. The second meiotic division only completes if fertilization occurs.
This means a woman releases roughly one egg per month, about 400 to 500 over a reproductive lifetime. Menopause, which typically occurs around age 50, marks the point when the supply of viable follicles is essentially exhausted and monthly ovulation stops.
The Hormones That Drive Production
Both sperm and egg production depend on the same two key hormones released by the pituitary gland in the brain: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The hypothalamus sits upstream, releasing a trigger hormone that tells the pituitary when and how much FSH and LH to produce.
In males, LH stimulates cells in the testes to produce testosterone, which is essential for maintaining sperm production. FSH supports the Sertoli cells that nurture developing sperm. The combination of testosterone and FSH is what initiates and sustains spermatogenesis from puberty onward.
In females, FSH is required for follicles to grow beyond their earliest resting stage. Without functional FSH signaling, follicles stall at a small, immature size, similar to what’s seen in prepubertal ovaries. LH triggers the final maturation of the egg and ovulation itself. The familiar hormonal shifts of the menstrual cycle reflect the rising and falling levels of these two hormones as they coordinate monthly egg development.
How Meiosis Creates Haploid Cells
The defining feature of gamete production is meiosis, the cell division process that reduces chromosome number. Human body cells carry 46 chromosomes (23 pairs). Gametes need exactly half that number so fertilization restores the full set.
Meiosis accomplishes this in two rounds. During the first round, paired chromosomes line up and are pulled to opposite sides of the cell. Each resulting daughter cell gets one chromosome from each pair, cutting the total from 46 to 23. This is the reduction step. The second round resembles a normal cell division: chromosomes split down the middle, but the total number stays at 23. The end result is four genetically unique haploid cells from one starting cell.
In sperm production, all four cells become functional sperm. In egg production, the divisions are unequal. Most of the cell’s contents are funneled into one large egg, while the leftover material forms tiny cells called polar bodies that degrade. This ensures the egg is packed with enough nutrients and cellular machinery to support early embryonic development.
How Plants Produce Gametes
Plants don’t have gonads, but they still produce sperm and eggs. The process differs from animals because plant life cycles alternate between two distinct body forms: a sporophyte (the plant you see) and a gametophyte (a smaller structure that produces gametes).
In simpler plants like mosses and ferns, the gametophyte is a visible, independent structure. It develops male organs called antheridia, which produce sperm through mitosis, and female organs called archegonia, which produce eggs. Ferns can produce both types on a single gametophyte. These sperm typically need a film of water to swim to the egg.
In flowering plants, the gametophytes are tiny and hidden inside the flower. The pollen grain is the male gametophyte, and a small cluster of cells inside the ovule is the female gametophyte. Flowering plants no longer rely on water for fertilization. Instead, pollen is delivered by wind, insects, or other carriers, and a pollen tube grows to deliver sperm directly to the egg. The flower itself is the structure that houses all the machinery for gamete production and fertilization in one place.