Learning Outcomes
Asexual reproduction occurs in prokaryotic microorganisms (bacteria) and in some eukaryotic single-celled and multi-celled organisms. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly. Show In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment. In an unstable or unpredictable environment asexually-reproducing species may be at a disadvantage because all the offspring are genetically identical and may not have the genetic variation to survive in new or different conditions. On the other hand, the rapid rates of asexual reproduction may allow for a speedy response to environmental changes if individuals have mutations. An additional advantage of asexual reproduction is that colonization of new habitats may be easier when an individual does not need to find a mate to reproduce. There are a number of ways that animals reproduce asexually. FissionFission, also called binary fission, occurs in prokaryotic microorganisms and in some invertebrate, multi-celled organisms. After a period of growth, an organism splits into two separate organisms. Some unicellular eukaryotic organisms undergo binary fission by mitosis. In other organisms, part of the individual separates and forms a second individual. This process occurs, for example, in many asteroid echinoderms through splitting of the central disk. Some sea anemones and some coral polyps (Figure 1a) also reproduce through fission. BuddingBudding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals. Budding occurs commonly in some invertebrate animals such as corals and hydras. In hydras, a bud forms that develops into an adult and breaks away from the main body, as illustrated in Figure 1b, whereas in coral budding, the bud does not detach and multiplies as part of a new colony.  Figure 1. (a) Coral polyps reproduce asexually by fission. (b) Hydra reproduce asexually through budding. (credit a: G. P. Schmahl, NOAA FGBNMS Manager)
Watch a video of a hydra budding. Note that there is no audio in this video. You can view the descriptive transcript for “Budding In Hydra” here (opens in new window). FragmentationFigure 2. Sea stars can reproduce through fragmentation. The large arm, a fragment from another sea star, is developing into a new individual. Fragmentation is the breaking of the body into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow. For example, in many sea stars, asexual reproduction is accomplished by fragmentation. Figure 2 illustrates a sea star for which an arm of the individual is broken off and regenerates a new sea star. Fisheries workers have been known to try to kill the sea stars eating their clam or oyster beds by cutting them in half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in twice as many sea stars to prey upon the oysters and clams. Fragmentation also occurs in annelid worms, turbellarians, and poriferans. Note that in fragmentation, there is generally a noticeable difference in the size of the individuals, whereas in fission, two individuals of approximate size are formed. ParthenogenesisParthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process and the species. Parthenogenesis occurs in invertebrates such as water flees, rotifers, aphids, stick insects, some ants, wasps, and bees. Bees use parthenogenesis to produce haploid males (drones) and diploid females (workers). If an egg is fertilized, a queen is produced. The queen bee controls the reproduction of the hive bees to regulate the type of bee produced. Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Although more common in plants, parthenogenesis has been observed in animal species that were segregated by sex in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males. Contribute!Did you have an idea for improving this content? We’d love your input. Improve this pageLearn More Binary fission may be as old as the very first forms of life – over 3.5 billion years old. However, the process has remained unchanged ever since then. Read on to explore binary fission in bacteria and amoeba reproduction in detail. Binary Fission Definition
What is Binary Fission?Binary fission is a type of asexual reproduction typically observed in prokaryotes and a few single-celled eukaryotes. In this method of asexual reproduction, there is a separation of the parent cell into two new daughter cells. This process happens with the division and duplication of the parent’s genetic matter into two parts. Here, each daughter cell receives one copy of its parent DNA. It is a primary method of reproduction in prokaryotic organisms. Binary Fission occurs without any spindle apparatus formation in the cell. In this process, the single DNA molecule begins replication and then attaches each copy to various parts of the cell membrane. When the cell starts to get drawn apart, the original (actual) and replicated chromosomes get apart. However, asexual mode of reproduction has a significant drawback. All resultant cells are genetically identical, mirror copies of each other and the parent cell. Most antibiotics work on this principle. If a parent cell is vulnerable to an antibiotic, then all resultant daughter cells are vulnerable too. If a mutation occurs in their genes, then it can render a particular strain resistant to antibiotics. Prokaryotes such as E. coli, Archaea as well as eukaryotes such as euglena reproduce through binary fission. Binary fission is a form of cell division in eukaryotes. In prokaryotes, it is a form of asexual reproduction Binary Fission in BacteriaThe process of binary fission is usually rapid, and its speed varies among species. The time required by bacteria to double the number of cells it has is called doubling time. Furthermore, each species requires specific conditions for its growth. These conditions include pH levels, temperature, oxygen, light, moisture, osmotic pressure. For instance, mesophiles thrive at moderate temperatures ranging from 20 °C to 45 °C. The ambient temperature of the human body is 37 °C, which means many of the disease-causing bacteria are mesophiles. Mycobacterium tuberculosis is the bacterium that causes tuberculosis in humans. It divides every 15 to 20 hours, which is very slow when compared to other pathogenic bacteria such as Escherichia coli, which can divide every 20 minutes. On the other end of the spectrum are the extremophiles. These bacteria can survive extremely harsh conditions such as high temperatures, high salinity, highly acidic environments and more. For instance, the Deinococcus radiodurans is an extremophilic bacteria that can survive a thousand times more radiation than a person can. Under normal circumstances, it can divide every 48 hours. However, when exposed to harsh conditions like drought, it can slow down its growth rate until more favourable conditions arise. Read more: Bacteria The steps involved in the binary fission in bacteria are: Step 1- Replication of DNAThe bacterium uncoils and replicates its chromosome, essentially doubling its content. Step 2- Growth of a CellAfter copying the chromosome, the bacterium starts to grow larger in preparation for binary fissions. It is followed by an increase in cytoplasmic content. Another prominent trait of this stage is that the two strands migrate to opposite poles of the cell. Step 3-Segregation of DNAThe cell elongates with a septum forming at the middle. The two chromosomes are also separated in this phase. Step 4- Splitting of CellsA new cell wall is formed at this phase, and the cell splits at the centre, dividing the parent cell into two new daughter cells. Each of the daughter cells contains a copy of the nuclear materials as necessary organelles. Amoeba Reproduction-Binary Fission in AmoebaAmoeba is a unicellular organism, and just like bacteria, it reproduces through binary fission. After replicating its genetic material through mitotic division, the cell divides into two equal-sized daughter cells. In this method, two similar individuals are produced from a single parent cell. An amoeba that is about to undergo division grows larger, and eventually, its nucleus extends and divides into two. The division of cytoplasm follows the division of the nucleus. So, two amoebae are produced from a single parent, and the parent’s identity is technically “lost.” Read More: Nutrition in Amoeba To know more, watch the video given below: Amoeba reproduces asexually through binary fission. In this process, an individual divides itself into two daughter cells. These are genetically identical to each other.
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Listed below are different types of Binary fission:
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What kind of asexual reproduction happens if an organism splits into two daughter organisms?
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