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'''Sexuality''' refers to a biologic state where reproduction is characterized by some manner of [[Sexual Intercourse|sexual union]] between the male and female of a species. This processes enables the passing of  a combination of [[Genetics|genetic]] [[material]] to offspring, resulting in [[creativity|creative]] diversity. The main two processes are: [[meiosis]], involving the halving of the number of [[chromosome]]s; and [[fertilization]], involving the [[fusion]] of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve genetic recombination.

'''Sexuality''' refers to a biologic state where reproduction is characterized by some manner of [[Sexual Intercourse|sexual union]] between the male and female of a species. This processes enables the passing of  a combination of [[Genetics|genetic]] [[material]] to offspring, resulting in [[creativity|creative]] diversity. The main two processes are: [[meiosis]], involving the halving of the number of [[chromosome]]s; and [[fertilization]], involving the [[fusion]] of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve genetic recombination.

The [[evolution]] of [http://www.biolreprod.org/ sexual reproduction] is a major puzzle. The first [http://proxy.arts.uci.edu/~nideffer/Hawking/early_proto/orgel.html] Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all [[animal]]s and [[plant]]s. Bacterial conjugation, the transfer of [[DNA]] between two bacteria, is often mistakenly confused with [[sexual reproduction]], because the mechanics are similar.

The [[evolution]] of [https://www.biolreprod.org/ sexual reproduction] is a major puzzle. The first [https://proxy.arts.uci.edu/~nideffer/Hawking/early_proto/orgel.html] Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all [[animal]]s and [[plant]]s. Bacterial conjugation, the transfer of [[DNA]] between two bacteria, is often mistakenly confused with [[sexual reproduction]], because the mechanics are similar.

<center>For lessons on the topic of '''''[[Sexuality]]''''' [https://nordan.daynal.org/wiki/index.php?title=Category:Sexuality follow this link].</center>

<center>For lessons on the topic of '''''[[Sexuality]]''''' [https://nordan.daynal.org/wiki/index.php?title=Category:Sexuality follow this link].</center>

A major question is why sexual reproduction persists when [[parthenogenesis]] appears in some ways to be a superior form of reproduction.  Contemporary [[evolution]]ary [[thought]] proposes some explanations.  It may be due to selection pressure on the [[clade]] itself—the ability for a population to radiate more rapidly in response to a changing environment through sexual recombination than parthenogenesis allows.  Alternatively, sexual reproduction may allow for the "ratcheting" of evolutionary speed as one clade competes with another for a limited resource.

A major question is why sexual reproduction persists when [[parthenogenesis]] appears in some ways to be a superior form of reproduction.  Contemporary [[evolution]]ary [[thought]] proposes some explanations.  It may be due to selection pressure on the [[clade]] itself—the ability for a population to radiate more rapidly in response to a changing environment through sexual recombination than parthenogenesis allows.  Alternatively, sexual reproduction may allow for the "ratcheting" of evolutionary speed as one clade competes with another for a limited resource.

Marsupials reproductive systems differ markedly from those of placental mammals. Females have two [[vagina]]s, both of which open externally through one orifice but lead to different compartments within the [[uterus]]. Males generally have a two-pronged [[penis]], which corresponds to the females' two vaginae. The penis is used only for discharging [[semen]] into females, and is separate from the urinary tract. Both sexes possess a [[cloaca]], which is connected to a urogenital sac used to store waste before expulsion.

Marsupials reproductive systems differ markedly from those of placental mammals. Females have two [[vagina]]s, both of which open externally through one orifice but lead to different compartments within the [[uterus]]. Males generally have a two-pronged [[penis]], which corresponds to the females' two vaginae. The penis is used only for discharging [[semen]] into females, and is separate from the urinary tract. Both sexes possess a [[cloaca]], which is connected to a urogenital sac used to store waste before expulsion.

The female develops a kind of [[yolk]] sack in her womb which delivers nutrients to the [[embryo]]. Embryos of [[bandicoots]], [[koalas]] and [[wombats]] additionally form [[placenta]]-like organs that connect them to the [[uterus|uterine]] wall, although the placenta-like organs are smaller than in placental mammals and it is not certain that they transfer nutrients from  the mother to the embryo. [http://animaldiversity.ummz.umich.edu/site/accounts/information/Peramelidae.html]  

The female develops a kind of [[yolk]] sack in her womb which delivers nutrients to the [[embryo]]. Embryos of [[bandicoots]], [[koalas]] and [[wombats]] additionally form [[placenta]]-like organs that connect them to the [[uterus|uterine]] wall, although the placenta-like organs are smaller than in placental mammals and it is not certain that they transfer nutrients from  the mother to the embryo. [https://animaldiversity.ummz.umich.edu/site/accounts/information/Peramelidae.html]  

Pregnancy is very short, typically 4 to 5 weeks. The embryo is born at a very young stage of development, and is usually less than 5" long at birth. It has been suggested that the short pregnancy is necessary to reduce the risk that the mother's immune system will attack the embryo.

Pregnancy is very short, typically 4 to 5 weeks. The embryo is born at a very young stage of development, and is usually less than 5" long at birth. It has been suggested that the short pregnancy is necessary to reduce the risk that the mother's immune system will attack the embryo.

==Fish==

==Fish==

The vast majority of fish species lay eggs that are then fertilized by the male, [http://www.seaworld.org/animal-info/info-books/bony-fish/reproduction.htm] some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column.   

The vast majority of fish species lay eggs that are then fertilized by the male, [https://www.seaworld.org/animal-info/info-books/bony-fish/reproduction.htm] some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column.   

Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fishes that have live-bearing offspring include the Guppy and Mollies or ''Poecilia''. Fishes that give birth to live young can be [[ovoviviparous]], where the eggs are fertilized within the female and the eggs simply hatch within the female body, or they can be [[viviparous]], where the female supplies nourishment to the internally growing offspring.  Some fish are [[hermaphrodite]]s, where a single fish is both male and female and can produce eggs and sperm. In hermaphroditic fish, some are male and female at the same time while in other fish they are serially hermaphroditic; starting as one sex and changing to the other. In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. One fish species does not need sexual reproduction to produce offspring; ''Poecilia formosa'' can use [[parthenogenesis]] for reproduction, where unfertilized eggs develop into embryos that produce female offspring.

Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fishes that have live-bearing offspring include the Guppy and Mollies or ''Poecilia''. Fishes that give birth to live young can be [[ovoviviparous]], where the eggs are fertilized within the female and the eggs simply hatch within the female body, or they can be [[viviparous]], where the female supplies nourishment to the internally growing offspring.  Some fish are [[hermaphrodite]]s, where a single fish is both male and female and can produce eggs and sperm. In hermaphroditic fish, some are male and female at the same time while in other fish they are serially hermaphroditic; starting as one sex and changing to the other. In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. One fish species does not need sexual reproduction to produce offspring; ''Poecilia formosa'' can use [[parthenogenesis]] for reproduction, where unfertilized eggs develop into embryos that produce female offspring.

==See also==

==See also==

*'''''[[Eroticism]]'''''

*'''''[[Eroticism]]'''''

*'''''[http://www.mhhe.com/socscience/sex/common/ibank/set-1.htm McGraw Hill Human Sexuality Image Bank]'''''

*'''''[https://www.mhhe.com/socscience/sex/common/ibank/set-1.htm McGraw Hill Human Sexuality Image Bank]'''''

*'''''[[Sexual Intercourse]]'''''

*'''''[[Sexual Intercourse]]'''''

*'''''[[Heterosexuality]]'''''

*'''''[[Heterosexuality]]'''''

==Notes==

==Notes==

#Orgel, Leslie E.. "The Origin of Life on the Earth". Scientific American. [http://proxy.arts.uci.edu/~nideffer/Hawking/early_proto/orgel.html].  

#Orgel, Leslie E.. "The Origin of Life on the Earth". Scientific American. [https://proxy.arts.uci.edu/~nideffer/Hawking/early_proto/orgel.html].  

#Lovett Doust, Jon, and Lesley Lovett Doust. 1988. Plant reproductive ecology: patterns and strategies. New York: Oxford University Press. P 290.

#Lovett Doust, Jon, and Lesley Lovett Doust. 1988. Plant reproductive ecology: patterns and strategies. New York: Oxford University Press. P 290.

#Iowa State University Biology Dept. Discoveries about Marsupial Reproduction Anna King 2001. webpage

#Iowa State University Biology Dept. Discoveries about Marsupial Reproduction Anna King 2001. webpage

# "Family Peramelidae (bandicoots and echymiperas)". [http://animaldiversity.ummz.umich.edu/site/accounts/information/Peramelidae.html].  

# "Family Peramelidae (bandicoots and echymiperas)". [https://animaldiversity.ummz.umich.edu/site/accounts/information/Peramelidae.html].  

#BONY FISHES - Reproduction

#BONY FISHES - Reproduction

#Orlando EF, Katsu Y, Miyagawa S, Iguchi T. J Mol Endocrinol. 2006 Oct;37(2):353-65. Cloning and differential expression of estrogen receptor and aromatase genes in the self-fertilizing hermaphrodite and male mangrove rivulus, Kryptolebias marmoratus. Department of Biological Sciences, Florida Atlantic University, North, Ft. Pierce, Florida 34946, USA. eorlando@fau.edu

#Orlando EF, Katsu Y, Miyagawa S, Iguchi T. J Mol Endocrinol. 2006 Oct;37(2):353-65. Cloning and differential expression of estrogen receptor and aromatase genes in the self-fertilizing hermaphrodite and male mangrove rivulus, Kryptolebias marmoratus. Department of Biological Sciences, Florida Atlantic University, North, Ft. Pierce, Florida 34946, USA. eorlando@fau.edu

==References==

==References==

# Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004

# Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004

# [http://www.biolreprod.org/ Journal of Biology of Reproduction], accessed in August 2005.

# [https://www.biolreprod.org/ Journal of Biology of Reproduction], accessed in August 2005.

[[Category: Biology]]

[[Category: Biology]]