Sexual reproduction
Sexual reproduction is a type of
Sexual reproduction is the most common life cycle in
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
Maintenance of sexual reproduction has been explained by theories that work at several
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
Animals
Arthropods
A few arthropods, such as
Insects
Insect species make up more than two-thirds of all
Mammals
There are three extant kinds of mammals:
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
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
Flowering plants
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
Bryophytes
The
Fungi
Bacteria and archaea
Three distinct processes in
Bacterial transformation involves the
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
- 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
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- ^ Woods, Kerry (June 19, 2012). "Flowering Plants". Encyclopedia of Life. Archived from the original on September 13, 2022. Retrieved September 12, 2022.
- PMID 21819940. Archived from the original on 2022-09-13. Retrieved 2022-09-13 – via Elsevier Science Direct.)
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- ^ Otto, Sarah (2014). "Sexual Reproduction and the Evolution of Sex". Scitable. Archived from the original on 28 January 2019. Retrieved 28 Feb 2019.
- ^ John Maynard Smith The Evolution of Sex 1978.
- ^ Ridley, M. (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.
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- ^ Cecie Starr (2013). Biology: The Unity and Diversity of Life (Ralph Taggart, Christine Evers, Lisa Starr ed.). Cengage Learning. p. 281.
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- ^ 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.
- ^ 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.
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Further reading
- Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004
- Journal of Biology of Reproduction, accessed in August 2005.
- "Sperm Use Heat Sensors To Find The Egg; Weizmann Institute Research Contributes To Understanding Of Human Fertilization", Science Daily, 3 February 2003
- Michod, R. E.; Levin, B.E., eds. (1987). The Evolution of sex: An examination of current ideas. Sunderland, Massachusetts: Sinauer Associates. ISBN 978-0-87893-458-4.
- Michod, R. E. (1994). Eros and Evolution: A Natural Philosophy of Sex. Perseus Books. ISBN 978-0-201-40754-9.