Warm-Up 3/2

1. Steps in oogenesis:

Oogenesis is the process by which oogonia (primitive female egg cell developed during fetal development) becomes a zygote (the result of the mating of sperm and egg). During the first phase, the oogonia start meiosis but are stopped at prophase meiosis I during fetal development. During the second phase, increasing levels of FSH (follicle stimulating hormone) during puberty cause the primary follicular cells to grow and start producing estrogen. In the third phase, the secondary oocyte begins meiosis II and stops in metaphase. A secondary oocyte is ovulated. If the oocyte is fertilized, meisosis II resumes. The oocyte splits into an ovum and a second polar body. The sperm and ovum unite and form a diploid zygote.

2. Steps of spermatogenesis:

Spermatogenesis is the process whereby the seminiferous tubules produce sperm. There are three steps in spermatogenesis: 1) meiosis, during which the number of chromosomes in the cell is reduced to half or 23 chromosomes each; 2) meiosis II, during which each haploid cell forms spermatids; and 3) spermiogenesis, during which each spermatid develops into a sperm cell with a head and tail. The entire process of spermatogenesis takes about 64 days.

3. 

Spermatogenesis	Oogenesis
Number of gametes
Principle: continuous production. Although from puberty to old age sperm cells are constantly being engendered, the production is subject to extreme fluctuations regarding both quantity and quality.	Principle: Using up the oocytes generated before birth. Continual decrease of the oocytes, beginning with the fetal period. Exhaustion of the supply at menopause.
Meiotic output
Four functioning, small (head 4 mm), motile spermatozoids at the end of the meiosis	One large, immotile oocyte (diameter 120 mm) and three shriveled polar bodies are left at the end of the meiosis
Fetal period
No meiotic divisions	Entering into meiosis (arrested in the dictyotene stage)
No germ cell production	Production of the entire supply of germ cells