What type of asexual reproduction occurs when an organism divides into several parts and the separated parts develop into an individual organism?

Sexual reproduction is the combination of (usually haploid) reproductive cells from two individuals to form a third (usually diploid) unique offspring. Sexual reproduction produces offspring with novel combinations of genes. This can be an adaptive advantage in unstable or unpredictable environments. As humans, we are used to thinking of animals as having two separate sexes—male and female—determined at conception. However, in the animal kingdom, there are many variations on this theme.

Hermaphroditism occurs in animals where one individual has both male and female reproductive parts. Invertebrates such as earthworms, slugs, tapeworms and snails, shown in Figure 24.5, are often hermaphroditic. Hermaphrodites may self-fertilize or may mate with another of their species, fertilizing each other and both producing offspring. Self fertilization is common in animals that have limited mobility or are not motile, such as barnacles and clams.

Mammalian sex determination is determined genetically by the presence of X and Y chromosomes. Individuals homozygous for X (XX) are female and heterozygous individuals (XY) are male. The presence of a Y chromosome causes the development of male characteristics and its absence results in female characteristics. The XY system is also found in some insects and plants.

Avian sex determination is dependent on the presence of Z and W chromosomes. Homozygous for Z (ZZ) results in a male and heterozygous (ZW) results in a female. The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects (such as butterflies and moths), and reptiles use this system.

The sex of some species is not determined by genetics but by some aspect of the environment. Sex determination in some crocodiles and turtles, for example, is often dependent on the temperature during critical periods of egg development. This is referred to as environmental sex determination, or more specifically as temperature-dependent sex determination. In many turtles, cooler temperatures during egg incubation produce males and warm temperatures produce females. In some crocodiles, moderate temperatures produce males and both warm and cool temperatures produce females. In some species, sex is both genetic- and temperature-dependent.

Individuals of some species change their sex during their lives, alternating between male and female. If the individual is female first, it is termed protogyny or “first female,” if it is male first, its termed protandry or “first male.” Oysters, for example, are born male, grow, and become female and lay eggs; some oyster species change sex multiple times.

Summary

Reproduction may be asexual when one individual produces genetically identical offspring, or sexual when the genetic material from two individuals is combined to produce genetically diverse offspring. Asexual reproduction occurs through fission, budding, and fragmentation. Sexual reproduction may mean the joining of sperm and eggs within animals’ bodies or it may mean the release of sperm and eggs into the environment. An individual may be one sex, or both; it may start out as one sex and switch during its life, or it may stay male or female.

1. Which form of reproduction is thought to be best in a stable environment?
   1. asexual
   2. sexual
   3. budding
   4. parthenogenesis
2. Which form of reproduction can result from damage to the original animal?
   1. asexual
   2. fragmentation
   3. budding
   4. parthenogenesis
3. Which form of reproduction is useful to an animal with little mobility that reproduces sexually?
   1. fission
   2. budding
   3. parthenogenesis
   4. hermaphroditism
4. Genetically unique individuals are produced through ________.
   1. sexual reproduction
   2. parthenogenesis
   3. budding
   4. fragmentation
5. Why is sexual reproduction useful if only half the animals can produce offspring and two separate cells must be combined to form a third?
6. What determines which sex will result in offspring of birds and mammals?

Answers

1. A
2. B
3. D
4. A
5. Sexual reproduction produces a new combination of genes in the offspring that may better enable them to survive changes in the environment and assist in the survival of the species.
6. The presence of the W chromosome in birds determines femaleness and the presence of the Y chromosome in mammals determines maleness. The absence of those chromosomes and the homogeneity of the offspring (ZZ or XX) leads to the development of the other sex.

Form of asexual reproduction

Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning, where an organism is split into fragments. Each of these fragments develops into mature, fully grown individuals that are clones of the original organism.

The organism may develop specific organs or zones to shed or be easily broken off. If the splitting occurs without the prior preparation of the organism, both fragments must be able to regenerate the complete organism for it to function as reproduction.

Fragmentation as a method of reproduction is seen in organisms such as filamentous cyanobacteria, molds, lichens, sponges, acoel flatworms, some annelid worms and sea stars.[1]

Fragmentation in various organisms

Molds, yeasts and mushrooms, all of which are part of the Fungi kingdom, produce tiny filaments called hyphae. These hyphae obtain food and nutrients from the body of other organisms to grow and fertilize. Then a piece of hyphae breaks off and grows into a new individual and the cycle continues.

Many lichens produce specialized structures that can easily break away and disperse. These structures contain both hyphae of the mycobiont and the algae (phycobiont) (see soredia and isidia). Larger fragments of the thallus may break away when the lichen dries or due to mechanical disturbances (see the section on reproduction in lichens).

Plants

Fragmentation is a very common type of vegetative reproduction in plants. Many trees, shrubs, nonwoody perennials, and ferns form clonal colonies by producing new rooted shoots by rhizomes or stolons, which increases the diameter of the colony. If a rooted shoot becomes detached from the colony, then fragmentation has occurred. There are several other mechanisms of natural fragmentation in plants.

• Production of specialized reproductive structures: A few plants produce adventitious plantlets on their leaves, which drop off and form independent plants, e.g. Tolmiea menziesii and Kalanchoe daigremontiana. Others produce organs like bulbils and turions.
• Easily lost parts that have high potential to grow into a complete plant: Some woody plants like the willow naturally shed twigs. This is termed cladoptosis. The lost twigs may form roots in a suitable environment to establish a new plant. River currents often tear off branch fragments from certain cottonwood species growing on riverbanks. Fragments reaching suitable environments can root and establish new plants.[2] Some cacti and other plants have jointed stems. When a stem segment, called a pad, falls off, it can root and form a new plant. Leaves of some plants readily root when they fall off, e.g. Sedum and Echeveria.
• Fragmentation is observed in nonvascular plants as well, for example, in liverworts and mosses. Small pieces of moss "stems" or "leaves" are often scattered by the wind, water or animals. If a moss fragment reaches a suitable environment, it can establish a new plant.[3] They also produce gemmae, for example in the splash-cups of Marchantia polymorpha,[4] that are easily broken off and distributed.

People use fragmentation to artificially propagate many plants via division, layering, cuttings, grafting, micropropagation and storage organs, such as bulbs, corms, tubers and rhizomes.

Animals

Sponges and coral colonies naturally fragment and reproduce. Many species of annelids and flatworms produce by this method. When the splitting occurs due to specific developmental changes, the terms orchiectomy, laparotomy, and budding are used. In'architomy' the animal splits at a particular point and the two fragments regenerate the missing organs and tissues. The splitting is not preceded by the development of the tissues to be lost. Before splitting, the animal may develop furrows at the zone of splitting. The headless fragment must regenerate a completely new head. In 'paratomy', the split occurs perpendicular to the antero-posterior axis and the split is preceded by the "pregeneration" of the anterior structures in the posterior portion. The two organisms have their body axis aligned i.e. they develop in a head to tail fashion. Budding is similar to paratomy except that the body axes need not be aligned: the new head may grow toward the side or even point backward (e.g. Convolutriloba retrogemma an acoel flat worm).[5][6]

Coral

Many types of coral colonies can increase in number by fragmentation occurring naturally[7] or artificially. Reef aquarium enthusiasts fragment corals for various purposes including shape control; sharing with others; regrowth experiments; and minimizing damage to natural coral reefs. Both hard and soft corals can be fragmented. Genera highly tolerant of fragmentation include Acropora, Montipora, Pocillopora, Euphyllia, and Caulastraea among others.[8] Most sea anemones reproduce through fragmentation via a variety of methods including longitudinal fission, where the original anemone splits across the middle forming two equal-sized anemones, and basal laceration, in which small parts of the animal split from the base to form new anemones.[9]

Echinoderms

In echinoderms, the process is usually known as fissiparity (a term also used infrequently for biological fission in general). Some species can intentionally reproduce in this manner through autotomy. This method is more common during the larval editing stages.[10]

Disadvantage of this process of reproduction

As this process is a form of asexual reproduction, it does not produce genetic diversity in the offspring. Therefore, these are more vulnerable to changing environments, parasites, and diseases.

See also

• Fission (biology)
• Budding
• Micropropagation

References

1. ^ "Fragmentation- Fragmentation in Animals and in Plants". BYJUS. Retrieved 2020-08-12.
2. ^ Rood, S.B., Kalischuk, M.L., and Braatne, J.H. 2003. Branch propagation, not cladoptosis, permits dispersive, clonal reproduction of riparian cottonwoods. Forest Ecology and Management 186: 227–242. [1] Archived 2007-09-28 at the Wayback Machine
3. ^ "Moss asexual reproduction". Archived from the original on 2006-09-27. Retrieved 2006-08-06.
4. ^ Equihua, Clementina (1987). "Diseminación de yemas en Marchantia polymorpha L. (Hepaticae)". Cryptogamie, Bryologie, Lichénologie (in Spanish). 8 (3): 199–217.
5. ^ Åkesson, Bertil; Robert Gschwentner; Jan Hendelberg; Peter Ladurner; Johann Müller; Reinhard Rieger (2001-12-01). "Fission in Convolutriloba longifissura: asexual reproduction in acoelous turbellarians revisited" (PDF). Acta Zoologica. 82 (3): 231–239. doi:10.1046/j.1463-6395.2001.00084.x. ISSN 1463-6395. Archived from the original (PDF) on 2016-03-04. Retrieved 2011-07-13.
6. ^ Egger, Bernhard (December 2008). "Regeneration: rewarding, but potentially risky" (PDF). Birth Defects Research Part C: Embryo Today: Reviews. 84 (4): 257–264. doi:10.1002/bdrc.20135. ISSN 1542-9768. PMID 19067421. Archived from the original (PDF) on 2011-08-11. Retrieved 2011-07-13.
7. ^ Lirman, Diego (2000-08-23). "Fragmentation in the branching coral Acropora palmata (Lamarck): growth, survivorship, and reproduction of colonies and fragments" (PDF). Journal of Experimental Marine Biology and Ecology. 251 (1): 41–57. doi:10.1016/s0022-0981(00)00205-7. ISSN 0022-0981. PMID 10958900. Retrieved 2011-07-13.
8. ^ Calfo, Anthony (2008). "Coral fragmentation: Not just for beginners". Reefkeeping Magazine. Reef Central. Retrieved 2015-05-03.
9. ^ "Fact Sheet: Sea Anemones". Marine Biological Association. Retrieved 3 September 2018.
10. ^ Helen Nilsson Sköld; Matthias Obst; Mattias Sköld; Bertil Åkesson (2009). "Stem Cells in Asexual Reproduction of Marine Invertebrates". In Baruch Rinkevich; Valeria Matranga (eds.). Stem Cells in Marine Organisms. Springer. p. 125. ISBN 978-90-481-2766-5.

Retrieved from "https://en.wikipedia.org/w/index.php?title=Fragmentation_(reproduction)&oldid=1114642540"