Sexual reproduction
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Sexual reproduction is a type of
reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that em ...

reproduction
that involves a complex
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...
in which a
gamete A gamete ( /ˈɡæmiːt/; from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the foll ...
(such as a
sperm Sperm is the male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual reproduction, reproduce sexuall ...

sperm
or
egg cell The egg cell, or ovum (plural ova), is the female reproductive Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproducti ...
) with a single set of
chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of ...

chromosome
s (
haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
) combines with another to produce a
zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈɡæmiːt/; from Ancient Gree ...

zygote
that develops into an organism composed of
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
with two sets of chromosomes (
diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
). Sexual reproduction is the most common life cycle in
multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biolo ...
eukaryotes Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline ...
, such as
animals Animals (also called Metazoa) are multicellular Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the L ...

animals
,
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

fungi
and
plants Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel t ...

plants
. Sexual reproduction does not occur in
prokaryote A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus, and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...
s (organisms without
cell nuclei In cell biology, the nucleus (pl. ''nuclei''; from Latin or , meaning ''kernel'' or ''seed'') is a biological membrane#Function, membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotes usually have a single nu ...
), but they have processes with similar effects such as
bacterial conjugation Bacterial conjugation is the transfer of genetic material between Bacteria, bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. This takes place through a pilus. It is a parasexual mode of reproduction in ...
,
transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Transf ...
and
transduction
transduction
, which may have been precursors to sexual reproduction in early eukaryotes. In the production of sex cells in eukaryotes, diploid mother cells divide to produce haploid cells known as gametes in a process called
meiosis spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division of germ cells in Sexual reproduction, sexually-reproducing organis ...

meiosis
that involves
genetic recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organism ...
. The
homologous chromosome A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pen ...
s pair up so that their
DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings ...

DNA
sequences are aligned with each other, and this is followed by exchange of genetic information between them. Two rounds of cell division then produce four haploid gametes, each with half the number of chromosomes from each parent cell, but with the genetic information in the parental chromosomes recombined. Two haploid gametes combine into one diploid cell known as a
zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈɡæmiːt/; from Ancient Gree ...

zygote
in a process called
fertilisation Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilisation
. The zygote incorporates genetic material from both gametes. Multiple
cell division Cell division is the process by which a parent cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious ...

cell division
s, without change of the number of chromosomes, then form a multicellular diploid phase or generation. In
human reproduction Human reproduction is any form of sexual reproduction Sexual reproduction is a type of reproduction that involves a complex Biological life cycle, life cycle in which a gamete (such as a sperm or egg cell) with a single set of chromosomes (haplo ...
, each cell contains 46 chromosomes in 23 pairs. Meiosis in the parents' gonads produces gametes that each contain only 23 chromosomes that are genetic recombinants of the DNA sequences contained in the parental chromosomes. When the nuclei of the gametes come together to form a fertilized egg or zygote, each cell of the resulting child will have 23 chromosomes from each parent, or 46 in total. In plants only, the diploid phase, known as the
sporophyte 350px, Sporophytes of moss during spring A sporophyte () is the diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
, produces spores by meiosis that germinate and then divide by mitosis to form a haploid multicellular phase, the
gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one ...
, that produces gametes directly by mitosis. This type of life cycle, involving alternation between two multicellular phases, the sexual haploid gametophyte and asexual diploid sporophyte, is known as
alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the type of life cycle that occurs in those plant Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by ...

alternation of generations
. The
evolution of sexual reproduction Evolution is change in the heritable characteristics of biological population In biology, a population is a number of all the organisms of the same group or species In biology, a species is the basic unit of biological classific ...
is considered paradoxical, because
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organis ...
should be able to outperform it as every young organism created can bear its own young. This implies that an asexual population has an intrinsic capacity to grow more rapidly with each generation.
John Maynard Smith John Maynard Smith (6 January 1920 – 19 April 2004) was a British theoretical and mathematical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War World War II or the Secon ...

John Maynard Smith
''The Evolution of Sex'' 1978.
This 50% cost is a fitness disadvantage of sexual reproduction. The two-fold cost of sex includes this cost and the fact that any organism can only pass on 50% of its own genes to its offspring. One definite advantage of sexual reproduction is that it impedes the accumulation of genetic
mutation A red tulip exhibiting a partially yellow petal due to a mutation in its genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...
s.
Sexual selection Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of the ...
is a mode of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable Phenotypic trait, traits characteristic of a populatio ...
in which some individuals out-reproduce others of a population because they are better at securing
mates Mates is an English surname, and may refer to: * James Mates (born 1964), British newsreader and journalist * Michael Mates (born 1934), British politician * Frederick S. Mates, founded the Mates Investment Fund in 1967 that crashed in the bear mar ...

mates
for sexual reproduction. It has been described as "a powerful evolutionary force that does not exist in asexual populations."


Evolution

The first
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the a ...

fossil
ized evidence of sexual reproduction in eukaryotes is from the
Stenian The Stenian Period (from grc, στενός, stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic era (geology), Era and lasted from annum, Mya to Mya (million years ago). Instead of being based on stratigraphy, these da ...
period, about 1.05  billion years ago. Biologists studying
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
propose several explanations for the development of sexual reproduction and its maintenance. These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of red queen hypothesis, adaptation to changing environments, tangled bank hypothesis, dealing with competition, DNA repair and masking deleterious mutations. All of these ideas about why sexual reproduction has been maintained are generally supported, but ultimately the size of the population determines if sexual reproduction is entirely beneficial. Larger populations appear to respond more quickly to some of the benefits obtained through sexual reproduction than do smaller population sizes. Maintenance of sexual reproduction has been explained by theories that work at several levels of selection, though some of these models remain controversial. However, newer models presented in recent years suggest a basic advantage for sexual reproduction in slowly reproducing complex organisms. Sexual reproduction allows these species to exhibit characteristics that depend on the specific Natural environment, environment that they inhabit, and the particular survival strategies that they employ.


Sexual selection

In order to reproduce sexually, both males and females need to find a mating, mate. Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway. Thus sexual reproduction, as a form of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable Phenotypic trait, traits characteristic of a populatio ...
, has an effect on
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
. Sexual dimorphism is where the basic phenotypic traits vary between males and females of the same species. Dimorphism is found in both sex organs and in secondary sex characteristics, body size, physical strength and morphology, biological ornamentation, behavior and other bodily traits. However, sexual selection is only implied over an extended period of time leading to sexual dimorphism.


Animals


Insects

Insect species make up more than two-thirds of all Extant taxon, extant animal species. Most insect species reproduce sexually, though some species are facultatively parthenogenetic. Many insects species have sexual dimorphism, while in others the sexes look nearly identical. Typically they have two sexes with males producing spermatozoa and females ova. The ova develop into eggs that have a covering called the chorion, which forms before internal fertilization. Insects have very diverse mating and reproductive strategies most often resulting in the male depositing spermatophore within the female, which she stores until she is ready for egg fertilization. After fertilization, and the formation of a zygote, and varying degrees of development, in many species the eggs are deposited outside the female; while in others, they develop further within the female and are born live.


Birds


Mammals

There are three extant kinds of mammals: monotremes, placentals and marsupials, all with internal fertilization. In placental mammals, offspring are born as juveniles: complete animals with the sex organs present although not reproductively functional. After several months or years, depending on the species, the sex organs develop further to maturity and the animal becomes Sexual maturity, sexually mature. Most female mammals are only fertility, fertile during certain periods during their estrous cycle, at which point they are ready to mate. Individual male and female mammals meet and carry out animal sexual behavior#Mammals, copulation. For most mammals, males and females Promiscuity, exchange sexual partners throughout their adult lives.Research conducted by Patricia Adair Gowaty. Reported by


Fish

The vast majority of fish species lay eggs that are then fertilized by the male. 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. Fish 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 in seahorses, the male carries the developing young within a pouch, and gives birth to live young. Fishes can also be viviparous, where the female supplies nourishment to the internally growing offspring. Some fish are hermaphrodites, 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 reproduce by sexual reproduction but uses sex to produce offspring; ''Poecilia formosa'' is a unisex species that uses a form of parthenogenesis called gynogenesis, where unfertilized eggs develop into embryos that produce female offspring. ''Poecilia formosa'' mate with males of other fish species that use internal fertilization, the sperm does not fertilize the eggs but stimulates the growth of the eggs which develops into embryos.


Reptiles


Amphibians


Mollusks


Plants

Animals have life cycles with a single diploid multicellular phase that produces haploid gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid adult. Plants have two multicellular life-cycle phases, resulting in an
alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the type of life cycle that occurs in those plant Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by ...

alternation of generations
. Plant zygotes germinate and divide repeatedly by mitosis to produce a diploid multicellular organism known as the sporophyte. The mature sporophyte produces haploid spores by meiosis that germinate and divide by mitosis to form a multicellular gametophyte phase that produces gametes at maturity. The gametophytes of different groups of plants vary in size. Mosses and other pteridophytic plants may have gametophytes consisting of several million cells, while angiosperms have as few as three cells in each pollen grain.


Flowering plants

Flowering plants are the dominant plant form on land and they reproduce either sexually or asexually. Often their most distinguishing feature is their reproductive organs, commonly called flowers. The Stamen, anther produces pollen, pollen grains which contain the male
gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one ...
s that produce sperm nuclei. For pollination to occur, pollen grains must attach to the stigma of the female reproductive structure (carpel), where the female gametophytes are located within ovules enclose within the ovary. After the pollen tube grows through the carpel's style, the sex cell nuclei from the pollen grain migrate into the ovule to fertilize the egg cell and endosperm nuclei within the female gametophyte in a process termed double fertilization. The resulting zygote develops into an embryo, while the triploid endosperm (one sperm cell plus two female cells) and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which produced the female gametophyte(s), then grows into a fruit, which surrounds the seed(s). Plants may either Self-pollination, self-pollinate or pollination, cross-pollinate. In 2013, flowers dating from the Cretaceous (100 million years before present) were found encased in amber, the oldest evidence of sexual reproduction in a flowering plant. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects. Nonflowering plants like ferns, moss and Marchantiophyta, liverworts use other means of sexual reproduction.


Ferns

Ferns produce large diploid
sporophyte 350px, Sporophytes of moss during spring A sporophyte () is the diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
s with rhizomes, roots and leaves. Fertile leaves produce sporangia that contain haploid spores. The spores are released and germinate to produce small, thin gametophytes that are typically heart shaped and green in color. The gametophyte Prothallus, prothalli, produce motile sperm in the antheridia and egg cells in archegonia on the same or different plants. After rains or when dew deposits a film of water, the motile sperm are splashed away from the antheridia, which are normally produced on the top side of the thallus, and swim in the film of water to the archegonia where they fertilize the egg. To promote out crossing or cross fertilization the sperm are released before the eggs are receptive of the sperm, making it more likely that the sperm will fertilize the eggs of different thallus. After fertilization, a
zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈɡæmiːt/; from Ancient Gree ...

zygote
is formed which grows into a new sporophytic plant. The condition of having separate sporophyte and gametophyte plants is called alternation of generations. Other plants with similar life cycles include ''Psilotum'', ''Lycopodium'' and ''Equisetum''.


Bryophytes

The bryophytes, which include Marchantiophyta, liverworts, hornworts and mosses, reproduce both sexually and Vegetative reproduction, vegetatively. They are small plants found growing in moist locations and like ferns, have motile sperm with flagella and need water to facilitate sexual reproduction. These plants start as a haploid spore that grows into the dominant gametophyte form, which is a multicellular haploid body with leaf-like structures that photosynthesis, photosynthesize. Haploid gametes are produced in antheridia (male) and archegonia (female) by mitosis. The sperm released from the antheridia respond to chemicals released by ripe archegonia and swim to them in a film of water and fertilize the egg cells thus producing a zygote. The
zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈɡæmiːt/; from Ancient Gree ...

zygote
divides by mitotic division and grows into a multicellular, diploid sporophyte. The sporophyte produces spore capsules (sporangia), which are connected by stalks (setae) to the archegonia. The spore capsules produce spores by meiosis and when ripe the capsules burst open to release the spores. Bryophytes show considerable variation in their reproductive structures and the above is a basic outline. Also in some species each plant is one sex (dioicous) while other species produce both sexes on the same plant (Monoicous, monoicous).


Fungi

Fungi are classified by the methods of sexual reproduction they employ. The outcome of sexual reproduction most often is the production of resting spores that are used to survive inclement times and to spread. There are typically three phases in the sexual reproduction of fungi: plasmogamy, karyogamy and
meiosis spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division of germ cells in Sexual reproduction, sexually-reproducing organis ...

meiosis
. The cytoplasm of two parent cells fuse during plasmogamy and the nuclei fuse during karyogamy. New haploid gametes are formed during meiosis and develop into spores. The adaptive basis for the maintenance of sexual reproduction in the Ascomycota and Basidiomycota (dikaryon) fungus, fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for maintaining this capability is the benefit of DNA repair, repairing DNA damage, caused by a variety of stresses, through homologous recombination, recombination that occurs during
meiosis spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division of germ cells in Sexual reproduction, sexually-reproducing organis ...

meiosis
.


Bacteria and archaea

Three distinct processes in
prokaryote A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus, and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...
s are regarded as similar to Origin and function of meiosis, eukaryotic sex: bacterial transformation, which involves the incorporation of foreign DNA into the bacterial chromosome;
bacterial conjugation Bacterial conjugation is the transfer of genetic material between Bacteria, bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. This takes place through a pilus. It is a parasexual mode of reproduction in ...
, which is a transfer of plasmid DNA between bacteria, but the plasmids are rarely incorporated into the bacterial chromosome; and Prokaryote#Gene transfer, gene transfer and genetic exchange in archaea. Bacterial transformation involves the genetic recombination, recombination of genetic material and its function is mainly associated with Sexual recombination#Recombinational repair, DNA repair. Bacterial transformation is a complex process encoded by numerous bacterial genes, and is a bacterial adaptation for DNA transfer. This process occurs naturally in at least 40 bacterial species. For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state referred to as competence (see Natural competence). Sexual reproduction in early single-celled eukaryotes may have evolved from bacterial transformation,Bernstein H, Bernstein C, Michod RE. (2012)
DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes
". Chapter 1, pp. 1–50, in ''DNA Repair: New Research'', Editors S. Kimura and Shimizu S. Nova Sci. Publ., Hauppauge, New York. Open access for reading only.
or from a similar process in archaea (see below). On the other hand, bacterial conjugation is a type of direct transfer of DNA between two bacteria mediated by an external appendage called the conjugation pilus. Bacterial conjugation is controlled by plasmid, plasmid genes that are adapted for spreading copies of the plasmid between bacteria. The infrequent integration of a plasmid into a host bacterial chromosome, and the subsequent transfer of a part of the host chromosome to another cell do not appear to be bacterial adaptations. Exposure of hyperthermophilic archaeal Sulfolobus species to DNA damaging conditions induces cellular aggregation accompanied by high frequency genetic marker exchange. Ajon et al. hypothesized that this cellular aggregation enhances species-specific DNA repair by homologous recombination. DNA transfer in ''Sulfolobus'' may be an early form of sexual interaction similar to the more well-studied bacterial transformation systems that also involve species-specific DNA transfer leading to homologous recombinational repair of DNA damage.


See also

*Amphimixis (psychology) *Anisogamy *Biological reproduction *Hermaphroditism *Isogamy *Mate choice *Mating in fungi *Operational sex ratio *Outcrossing *Allogamy *Self-incompatibility *Sex *Sexual intercourse *Transformation (genetics)


References


Further reading

* Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004
Journal of Biology of Reproduction
accessed in August 2005.

''Science Daily'', 3 February 2003 * *


External links


Khan Academy, video lecture
{{Authority control Sexual reproduction, Developmental biology Fertility Reproduction Sexuality