Sexual reproduction

Source: Wikipedia, the free encyclopedia.
haploid number (n). During fertilisation, haploid gametes come together to form a diploid zygote
, and the original number of chromosomes is restored.

Sexual reproduction is a type of

diploid).[1] This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.[2][3]

Sexual reproduction is the most common life cycle in

cell nuclei, such as bacteria and archaea. However, some processes in bacteria, including bacterial conjugation, transformation and transduction, may be considered analogous to sexual reproduction in that they incorporate new genetic information.[7] Some proteins and other features that are key for sexual reproduction may have arisen in bacteria, but sexual reproduction is believed to have developed in an ancient eukaryotic ancestor.[8]

In eukaryotes, diploid precursor cells divide to produce haploid cells in a process called meiosis. In meiosis, DNA is replicated to produce a total of four copies of each chromosome. This is followed by two cell divisions to generate haploid gametes. After the DNA is replicated in meiosis, the homologous chromosomes pair up so that their DNA sequences are aligned with each other. During this period before cell divisions, genetic information is exchanged between homologous chromosomes in genetic recombination. Homologous chromosomes contain highly similar but not identical information, and by exchanging similar but not identical regions, genetic recombination increases genetic diversity among future generations.[9]

During sexual reproduction, two haploid gametes combine into one diploid cell known as a zygote in a process called fertilization. The nuclei from the gametes fuse, and each gamete contributes half of the genetic material of the zygote. Multiple cell divisions by mitosis (without change in the number of chromosomes) then develop into a multicellular diploid phase or generation. In plants, the diploid phase, known as the sporophyte, produces spores by meiosis. These spores then germinate and divide by mitosis to form a haploid multicellular phase, the gametophyte, which 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.

The evolution of sexual reproduction is considered paradoxical,[10] because asexual reproduction 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.[11] This 50% cost is a fitness disadvantage of sexual reproduction.[12] 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. However, one definite advantage of sexual reproduction is that it increases genetic diversity and impedes the accumulation of harmful genetic mutations.[13][9]

Sexual selection is a mode of natural selection in which some individuals out-reproduce others of a population because they are better at securing mates interest for sexual reproduction.[14][failed verification][15] It has been described as "a powerful evolutionary force that does not exist in asexual populations".[16]

Evolution

The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1.05 billion years old.[17][18]

Biologists studying

dealing with competition, DNA repair, masking deleterious mutations, and reducing genetic variation on the genomic level.[20][21][22][23] 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.[24]

Maintenance of sexual reproduction has been explained by theories that work at several

complex organisms
.

Sexual reproduction allows these species to exhibit characteristics that depend on the specific environment that they inhabit, and the particular survival strategies that they employ.[25]

Sexual selection

In order to reproduce sexually, both males and females need to find a

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.[26]

Animals

Arthropods

Aphid giving birth to live young from an unfertilized egg
Harvestmen mating

A few arthropods, such as

hermaphroditic, that is, each can have the organs of both sexes. However, individuals of most species remain of one sex their entire lives.[27] A few species of insects and crustaceans can reproduce by parthenogenesis, especially if conditions favor a "population explosion". However, most arthropods rely on sexual reproduction, and parthenogenetic species often revert to sexual reproduction when conditions become less favorable.[28] The ability to undergo meiosis is widespread among arthropods including both those that reproduce sexually and those that reproduce parthenogenetically.[29] Although meiosis is a major characteristic of arthropods, understanding of its fundamental adaptive benefit has long been regarded as an unresolved problem,[30]
that appears to have remained unsettled.

ova remain in the female's body and the sperm must somehow be inserted. All known terrestrial arthropods use internal fertilization. Opiliones (harvestmen), millipedes, and some crustaceans use modified appendages such as gonopods or penises to transfer the sperm directly to the female. However, most male terrestrial arthropods produce spermatophores, waterproof packets of sperm, which the females take into their bodies. A few such species rely on females to find spermatophores that have already been deposited on the ground, but in most cases males only deposit spermatophores when complex courtship rituals look likely to be successful.[27]

penaeid shrimp
Most arthropods lay eggs,
nauplius larvae that have only three segments and pairs of appendages.[27]

Insects

An Australian emperor dragonfly laying eggs, guarded by a male

Insect species make up more than two-thirds of all

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.[35]

Mammals

There are three extant kinds of mammals:

copulation.[36] For most mammals, males and females exchange sexual partners throughout their adult lives.[37][38][39]

Fish

The vast majority of fish species lay eggs that are then fertilized by the male.[40] 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

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.[43]

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

angiosperms
have as few as three cells in each pollen grain.

Flowering plants

Flowers contain the sexual organs of flowering plants.

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-pollinate or 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.[45]

Ferns

Ferns produce large diploid

alternation of generations
.

Bryophytes

The

monoicous).[47]

Fungi

Puffballs emitting spores

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. 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) fungi was reviewed by Wallen and Perlin.[48] They concluded that the most plausible reason for maintaining this capability is the benefit of repairing DNA damage, caused by a variety of stresses, through recombination that occurs during meiosis.[48]

Bacteria and archaea

Three distinct processes in

bacterial transformation, which involves the incorporation of foreign DNA into the bacterial chromosome; bacterial conjugation, which is a transfer of plasmid DNA between bacteria, but the plasmids are rarely incorporated into the bacterial chromosome; and gene transfer and genetic exchange in archaea
.

Bacterial transformation involves the

DNA repair. Bacterial transformation is a complex process encoded by numerous bacterial genes, and is a bacterial adaptation for DNA transfer.[20][21] This process occurs naturally in at least 40 bacterial species.[49] 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,[22] 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.[50] Bacterial conjugation is controlled by 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.[20][51]

Exposure of hyperthermophilic archaeal Sulfolobus species to DNA damaging conditions induces cellular aggregation accompanied by high frequency genetic marker exchange[52][53] Ajon et al.[53] 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

References

  1. ^ John Maynard Smith & Eörz Szathmáry, The Major Transitions in Evolution, W. H. Freeman and Company, 1995, p 149
  2. ^ from the original on 2022-09-13. Retrieved 2022-09-13 – via Cold Spring Harbor.
  3. .
  4. .
  5. ^ Woods, Kerry (June 19, 2012). "Flowering Plants". Encyclopedia of Life. Archived from the original on September 13, 2022. Retrieved September 12, 2022.
  6. PMID 21819940. Archived from the original on 2022-09-13. Retrieved 2022-09-13 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: DOI inactive as of March 2024 (link
    )
  7. .
  8. .
  9. ^ a b "DNA Is Constantly Changing through the Process of Recombination". Nature. 2014. Archived from the original on September 15, 2022. Retrieved September 14, 2022.
  10. ^ Otto, Sarah (2014). "Sexual Reproduction and the Evolution of Sex". Scitable. Archived from the original on 28 January 2019. Retrieved 28 Feb 2019.
  11. ^ John Maynard Smith The Evolution of Sex 1978.
  12. ^ Ridley, M. (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.
  13. from the original on 20 January 2021. Retrieved 7 March 2021.
  14. ^ Cecie Starr (2013). Biology: The Unity and Diversity of Life (Ralph Taggart, Christine Evers, Lisa Starr ed.). Cengage Learning. p. 281.
  15. ^ Vogt, Yngve (January 29, 2014). "Large testicles are linked to infidelity". Phys.org. Archived from the original on November 12, 2020. Retrieved January 31, 2014.
  16. S2CID 4312385
    .
  17. from the original on 2016-10-23. Retrieved 2013-11-03.
  18. from the original on 2022-11-14. Retrieved 2021-10-28.
  19. .
  20. ^ (PDF) from the original on 2016-12-30. Retrieved 2013-04-22.
  21. ^ .
  22. ^
  23. .
  24. .
  25. .
  26. ^ Dimijian, G. G. (2005). Evolution of sexuality: biology and behavior. Proceedings (Baylor University. Medical Center), 18, 244–258.
  27. ^ a b c d Ruppert, Fox & Barnes (2004), pp. 537–539
  28. .
  29. .
  30. .
  31. ^ "Facts About Horseshoe Crabs and FAQ". Retrieved 2020-01-19.
  32. (PDF) from the original on 2008-10-03, retrieved 2008-09-28
  33. (PDF) from the original on 2008-10-03. Retrieved 2008-09-28.
  34. ^ Smith, G., Diversity and Adaptations of the Aquatic Insects (PDF), New College of Florida, archived from the original (PDF) on 3 October 2008, retrieved 2008-09-28
  35. .
  36. ^ Preston, Elizabeth (13 February 2024). "Self-Love Is Important, but We Mammals Are Stuck With Sex - Some female birds, reptiles and other animals can make a baby on their own. But for mammals like us, eggs and sperm need each other". The New York Times. Archived from the original on 13 February 2024. Retrieved 16 February 2024.
  37. ^ Reichard, U.H. (2002). "Monogamy—A variable relationship" (PDF). Max Planck Research. 3: 62–7. Archived from the original (PDF) on 24 May 2013. Retrieved 24 April 2013.
  38. .
  39. .
  40. ^ "BONY FISHES – Reproduction". Archived from the original on 2013-10-03. Retrieved 2008-02-11.
  41. . Retrieved 2013-11-03.
  42. .
  43. .
  44. .
  45. ^ Poinar, George O. Jr.; Chambers, Kenton L.; Wunderlich, Joerg (10 December 2013). "Micropetasos, a new genus of angiosperms from mid-Cretaceous Burmese amber". Journal of the Botanical Research Institute of Texas. 7 (2): 745–750. Archived from the original on 5 January 2014.
  46. ^ "Fern Reproduction". U.S. Forest Service. Archived from the original on 24 April 2023. Retrieved 24 April 2023.
  47. .
  48. ^ .
  49. .
  50. .
  51. .
  52. .
  53. ^ (PDF) from the original on 10 October 2021. Retrieved 13 December 2019.

Further reading

External links