Gametes are formed in the gonads; male testis and female ovary by the mechanism of meiotic cell division. The generation of gametes, and their regulation, is substantially different in males and females.
After puberty, both gonads also synthesis and secrete sex hormones into the bloodstream.
NCBI Bookshelf - Endocrinology: An Integrated Approach. Nussey, S.S. and Whitehead, S.A. Oxford, UK: BIOS Scientific Publishers, Ltd; 2001.
In females, the total number of eggs ever to be produced are present in the newborn female.
1.All eggs are arrested at an early stage of the first meiotic division as a primary oocyte. Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis 1 the day before ovulation.
2. In meosis 1, a diploid cell becomes 2 haploid daughter cells. One cell becomes the secondary oocyte the other the first polar body.
3. The secondary oocyte then undergoes meiosis 2 which arrests at metaphase and will not continue without fertilization.
Ovulation releases this oocyte from the ovary.
In males, sperm continues to be generated throughout life from a stem cell population in the testis.
Text: Sperm Are Produced Continuously in Many Mammals
Image: Figure 20-23. Cytoplasmic bridges in developing sperm cells and their precursors.
Spermatogenesis process of spermatagonia mature into spermatazoa (sperm).
Continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes).
At puberty spermatagonia activate and proliferate (mitosis).
primary spermatocyte -> secondary spermatocyte-> spermatid->sperm
Maturation involves meiosis and spermeogenesis
Ejeculate: 200-600 million sperm, 3.5 ml ; By volume < 10 % sperm (Accessory Glands, 60 % seminal vesicle, 10 % bulbourethral, 30 % prostate)
Abnormalities: Oligospermia (Low Sperm Count) less than 20 million sperm after 72 hour abstinence from sex, Azoospermia (Absent Sperm) blockage of duct network, Immotile Cilia Syndrome lack of sperm motility.
Female oogenesis
Meiosis initiated once in a finite population of cells
1 gamete produced / meiosis
Completion of meiosis delayed for months or years
Meiosis arrested at 1st meiotic prophase and reinitiated in a smaller population of cells
Differentiation of gamete occurs while diploid (in first meiotic prophase)
All chromosomes exhibit equivalent transcription and recombination during meiotic prophase
Male spermatogenesis
Meiosis initiated continuously in a mitotically dividing stem cell population
4 gametes produced / meiosis
Meiosis completed in days or weeks
Meiosis and differentiation proceed continuously without cell cycle arrest
Differentiation of gamete occurs while haploid (after meiosis ends)
Sex chromosomes excluded from recombination and transcription during first meiotic prophase
Link to next page in this Practical 3 - Fertilization
See Also: Male Sex Determination (sry) and Female X Inactivation (xist)
XY male genotype
There are several different nomenclatures for the stages of follicle maturation.
Atresia
At any one time the majority of follicles are destined not to complete maturation and at any stage (from type 4-7) degeneration of the follicle can occur. This process is called ATRESIA.
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Mitosis and Meiosis: MBoC Fig 20-6
Oogenesis: MBoC ch20f16.gif
Spermatogenesis: Dev Biol Ch19f18.jpg
Seminiferous Tubule: Dev Biol ch19f17.jpg
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