Human Gametogenesis

Spermatogenesis Is the production of sperm in testes. When males reach sexual maturity (puberty), diploid spermatocytes undergo meiosis to produce haploid sperm. Each sperm possesses a flagellum, which enables it to move. Males can produce 1 billion sperm/day! Some spermatocytes continue to undergo mitosis to create a constant supply of cells with which to produce sperm.

Spermatogenesis First meiotic division Second meiotic division

Oogenesis Is the production of eggs in the ovaries. At birth, a female will have all of the oocytes she will ever have. When females reach sexual maturity (puberty), each month a diploid oocyte undergo meiosis to produce one egg.

Oogenesis, cont’d The end products of oogenesis are: one large, haploid ootid which becomes the mature ovum (egg) three small, haploid polar bodies which disintegrate and die Cytokinesis is unequal - the ootid gets most of the cytoplasm and organelles to ensure the survival of the offspring should the egg be fertilized.

Oogenesis First meiotic division Second meiotic division

Oogenesis, cont’d As a female ages, the number of oocytes declines until age 50-60. Menopause occurs when the ovaries stop releasing eggs.

Diverse Gametes How the chromosomes line up at the middle of the cell during Metaphase I and II is completely random. The formula to calculate the number of combinations is 2n For humans, n is 23. So 223 is: over 8 million different combinations of chromosomes in gametes!! That’s why no two of us are the same – like snowflakes!

Fertility/Infertility Fertility is the ability to conceive through sexual intercourse. Infertility is defined as the inability to conceive within the period of one year. Assisted reproductive technology (ART) includes several therapies which address unique causes of infertility. These procedures are usually paired with more conventional therapies, such as fertility drugs, to increase success rates. In-vitro fertilization (IVF) - one of the most commonly used procedures. Eggs are combined with a partner's sperm in a dish in a laboratory. Once fertilization has occurred, the resulting embryos develop for 3 to 5 days before being placed in the uterus.