Misplaced Pages

• Bulbourethral glands
• Epididymis
• Penis
  • Foreskin
  • Frenulum of penis
  • Glans penis
• Prostate
• Scrotum
• Seminal vesicles
• Testicles

• Bartholin's glands
• Fallopian tubes
• Ovaries
• Skene's gland
• Uterus
  • Cervix
• Vagina
• Vulva
  • Hymen
  • Clitoris
    • Clitoral frenulum
    • Clitoral glans (glans clitoridis)
    • Clitoral hood
  • Labia
    • Labia majora
    • Labia minora
      • Frenulum of labia minora

Development

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In typical prenatal development, sex organs originate from a common primordium during early gestation and differentiate into male or female sexes. The SRY gene, usually located on the Y chromosome and encoding the testis determining factor, determines the direction of the differentiation. The absence of it allows the gonads to continue to develop into ovaries.

The development of the internal, and external reproductive organs is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them. The initial appearance of the fetal genitalia looks female-like: a pair of urogenital folds with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes and the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings grow, wrap around the penis, and fuse in the midline to form the penile urethra. Each sex organ in one sex has a homologous counterpart.

The process of sexual differentiation includes development of secondary sexual characteristics, such as patterns of pubic and facial hair and female breasts that emerge at puberty.

Because of the strong sexual selection affecting the structure and function of genitalia, they form an organ system that evolves rapidly. A great variety of genital form and function may therefore be found among animals.

Other animals

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In many other animals a single posterior orifice, called the cloaca, serves as the only opening for the reproductive, digestive, and urinary tracts (if present). All amphibians, birds, reptiles, some fish, and a few mammals (monotremes, tenrecs, golden moles, and marsupial moles) have this orifice, from which they excrete both urine and feces in addition to serving reproductive functions. Excretory systems with analogous purpose in certain invertebrates are also sometimes referred to as cloacae.

Insects

The organs concerned with insect mating and the deposition of eggs are known collectively as the external genitalia, although they may be largely internal; their components are very diverse in form.

Slugs and snails

The reproductive system of gastropods (slugs and snails) varies greatly from one group to another.

Planaria

Planaria are flat worms widely used in biological research. There are sexual and asexual planaria. Sexual planaria are hermaphrodites, possessing both testicles and ovaries. Each planarian transports its excretion to the other planarian, giving and receiving sperm.

Plants

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In most plant species an individual has both male and female sex organs.

The life cycle of land plants involves alternation of generations between a sporophyte and a haploid gametophyte. The gametophyte produces sperm or egg cells by mitosis. The sporophyte produces spores by meiosis which in turn develop into gametophytes. Any sex organs that are produced by the plant will develop on the gametophyte. The seed plants, which include conifers and flowering plants have small gametophytes that develop inside the pollen grains (male) and the ovule (female).

Flowering plants

In flowering plants the flowers contain the sex organs.

Sexual reproduction in flowering plants involves the union of the male and female germ cells, sperm and egg cells respectively. Pollen is produced in stamens, and is carried to the pistil, which has the ovary at its base where fertilization can take place. Within each pollen grain is a male gametophyte which consists of only three cells. In most flowering plants the female gametophyte within the ovule consists of only seven cells. Thus there are no sex organs as such.

Fungi

The sex organs in fungi are called gametangia. In some fungi the sex organs are indistinguishable from each other but in other cases male and female sex organs are clearly different.

Similar gametangia that are similar are called isogametangia. While male and female gametangia are called heterogametangia, which occurs in the majority of fungi.

See also

• Andrology
• Emasculation
• Genital modification and mutilation
• Hermaphrodite
• Human sexuality
• Hysterectomy
• Intimate part
• Obstetrics and gynaecology
• Oophorectomy
• Orchiectomy

References

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2. "Mosses and Ferns". Biology.clc.uc.edu. 16 March 2001. Archived from the original on 28 July 2012. Retrieved 1 August 2012.
3. "Flowering Plant Reproduction". Emc.maricopa.edu. 18 May 2010. Retrieved 1 August 2012.
4. Eberhard, W.G., 1985. Sexual Selection and Animal Genitalia. Harvard University Press
5. Schmidt-Rhaesa, Andreas (30 August 2007). The Evolution of Organ Systems. Oxford University Press. p. 252. ISBN 978-0-19-856668-7.
6. switze, International Conference on Comparative Physiology 1992 Crans; Bassau, Short & (4 August 1994). The Differences Between the Sexes. Cambridge University Press. p. 54. ISBN 978-0-521-44878-9.{{cite book}}: CS1 maint: numeric names: authors list (link)
7. Langerhans, R. Brian; Anderson, Christopher M.; Heinen-Kay, Justa L. (6 September 2016). "Causes and Consequences of Genital Evolution". Integrative and Comparative Biology. 56 (4): 741–751. doi:10.1093/icb/icw101. ISSN 1540-7063. PMID 27600556.
8. Simmons, Leigh W. (2014). "Sexual selection and genital evolution". Austral Entomology. 53 (1): 1–17. doi:10.1111/aen.12053. ISSN 2052-1758. S2CID 53690631.
9. Marvalee H. Wake (1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. p. 583. ISBN 978-0-226-87013-7.
10. Brigitta Olsen (15 November 2009). Daphne's Dance: True Tales in the Evolution of Woman's Sexual Awareness. Brigitta Olsen. p. 9. ISBN 978-0-9842117-0-8.
11. Anita Allen (November 2011). Unpopular Privacy: What Must We Hide?. Oxford University Press, USA. p. 219. ISBN 978-0-19-514137-5.
12. Hosken, David J., and Paula Stockley."Sexual selection and genital evolution." Archived 12 October 2017 at the Wayback Machine Trends in Ecology & Evolution 19.2 (2004): 87-93.
13. Arnqvist, Göran. "Comparative evidence for the evolution of genitalia by sexual selection." Archived 27 January 2012 at the Wayback Machine Nature 393.6687 (1998): 784.
14. Schilthuizen, M. 2014. Nature's Nether Regions: What the Sex Lives of Bugs, Birds, and Beasts Tell Us About Evolution, Biodiversity, and Ourselves. Penguin USA
15. "Male reproductive behaviour of Naja oxiana (Eichwald, 1831) in captivity, with a case of unilateral hemipenile prolapse". 2018 – via https://www.biotaxa.org/hn/article/view/34541. {{cite journal}}: Cite journal requires |journal= (help); External link in |via= (help)
16. Purves, William K.; Sadava, David E.; Orians, Gordon H.; Heller, H. Craig (2001). Life: The Science of Biology. Macmillan. p. 176. ISBN 978-0-7167-3873-2.
17. Purves, William K.; Sadava, David E.; Orians, Gordon H.; Heller, H. Craig (2001). Life: The Science of Biology. Macmillan. p. 665. ISBN 978-0-7167-3873-2.
18. Heritage, J.; Evans, E. G. V.; Killington, R. A. (26 January 1996). Introductory Microbiology. Cambridge University Press. p. 19. ISBN 978-0-521-44977-9.
19. Manoharachary, C.; Tilak, K. V. B. R.; Mallaiah, K. V.; Kunwar, I. K. (1 May 2016). Mycology and Microbiology (A Textbook for UG and PG Courses). Scientific Publishers. p. 328. ISBN 978-93-86102-13-3.

Further reading

• The Evolution of Primary Sexual Characters in Animals. Oxford: Oxford University Press. 2010. ISBN 978-0199717033. {{cite book}}: Unknown parameter |authors= ignored (help)