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Introduction:

What is asexual reproduction?
Asexual reproduction is a form of reproduction which requires only one parent. Unlike sexual reproduction, there is no exchange of genetic material or fertilization. Therefore, organisms that result from asexual reproduction will have the exact same DNA as their parent. Asexual reproduction is the simplest form of reproduction, since organisms are only making genetically identical copies of themselves. Asexual reproduction is also quite energy efficient, since organisms don’t need to spend the energy on finding a mate.
Asexual reproduction is seen as a natural method of reproduction among many different organisms in the world. It is a very common method of reproduction among less complex organisms and many higher organisms. Among the examples of asexual reproduction that we can see in the living world , there are many different methods of asexual reproduction. If we compare the reproduction of bacteria to the reproduction of yeast, for instance, we will be able to notice large differences.


Binary fission:
The first method of asexual reproduction that we will explore is called binary fission. In binary fission a single celled organism replicates its DNA and then divides itself into two separate cells. Each new cell will have the same DNA as the original cell. If the cell has organelles, half the organelles will be found in one of the daughter cells, and the other half will be found in the other daughter cell.

Binary fission is seen among prokaryotic cells such as bacteria. Bacteria do not have a nucleus, and their DNA only has one chromosome. Bacteria do not have mitochondria or chloroplasts, but they do have many ribosomes. When bacteria reproduce by binary fission, roughly half of these ribosomes will be found in each of the two daughter cells. The daughter cells will grow and make more ribosomes before dividing again.
Binary fission is a very efficient method of reproduction. E. coli, for instance, can divide as often as every 20 minutes. That means that when the living conditions are best for E. coli bacteria, they will grow and make more ribosomes and then copy all of their DNA at an incredibly fast pace before undergoing binary fission to create two identical cells.
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Shown here; a simple bacteria cell undergoing the process of binary fission. After binary fission, the resulting cells are the same size and have identical genetic information.
Why is binary fission important?
Since binary fission is an efficient method of asexual reproduction, the genetic information of one bacteria can quickly be multiplied. That means that if one bacteria has a genetic mutation that gives it an advantage in an environment, it will flourish and reproduce. The daughter cells will have this same genetic mutation, and they will both grow and then reproduce as well. The four cells that result from those two cells splitting will then also grow and reproduce. In other words, since binary fission is an energy efficient method of reproduction, in a short period of time there could be a large number of identical offspring from a single bacteria.




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Here, the rapid accumulation of bacterial cells in a short period of time is seen




Budding

Yeast
Yeast cells reproduce by a process called budding. This process is not to be confused with plant growth or germination—this natural method of reproduction is seen in a different kingdom altogether!

Budding in yeast cells is similar to the binary fission seen in bacteria, but there is an important difference. In budding, the daughter organism begins its life much smaller than the mother organism. Just like how binary fission starts, budding begins with a replication of the DNA. However, unlike how bacteria split into two equal portions, yeast cells begin to reproduce by pushing their DNA outward into a small region to its side. This region becomes a distinct ‘bud’ off of the mother cell. The bud will grow and develop as it receives nourishment from the mother cell. Eventually, the daughter cell will be big enough to break off and survive on its own. The final result will be two cells that are genetically identical, but the daughter cell will be a bit smaller than the mother cell when it first breaks off.


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Yeast cells can reproduce asexually through a method called budding.





Hydra
Hydras are simple, hollow organisms which live in fresh water systems such as lakes, streams, and ponds or rivers. They are usually only a few millimeters long and are able to be easily seen with a microscope. Hydras have a tubular body that is topped with tentacles. They have a primitive nervous system, and move in a tumbling or cartwheel motion by continually bending their body over and gripping the surface that they are living on. They have a mouth area in the center of their tentacles, and a digestive region in the center of their tubular body. Hydras eat small aquatic insects by catching them with their tentacles and bringing them into their mouth.

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Hydras are small water-dwelling organism. They reproduce both sexually and asexually.



Hydras can reproduce both sexually and asexually. Their method of asexual reproduction is the same method that yeast cells use to reproduce: budding. An adult hydra will begin the process of budding by producing a bulging region along their tubular body. This bulging region will grow and develop and form small tentacles at its tip. The small region will continue to grow and develop until it is large enough to support itself. Eventually the daughter hydra will break off from the mother hydra and will be free-living. The daughter hydra, being produced asexually, will be genetically identical to the mother hydra, but will begin its independent life smaller than its mother.

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An adult hydra will produce a tiny bud on its tubular body. In time, this bud will grow to become a daughter hydra.




Sporulation:
You’ve likely seen a piece of bread, cheese, or even fruit with white-ish green mold on it. What you probably didn’t know is that the mold that you see is actually an entire colony of millions of small individual fungus bodies. In reality, the moldy bread likely has fungus growing all over it by the time you see an entire colony.
Bread mold spreads by air-born spores. Spores are single cells that contain a full copy of the parent organisms DNA. Spores are specialized cells that are able to remain dormant for a period before germinating and growing. The fungus' spores are extremely tiny and can travel long distances by being blown through the air. These spores will germinate when they land on a suitable food source and will grow tiny hyphae into their food to gather nutrients. Hyphae are small specialized roots that help the fungus literally eat its food source. As the fungus grows and develops, it will grow what are called sporangia which are tall, skinny, spore-bearing structures. As these sporangia develop, they will release spores, which will spread to a new food source and continue the life cycle of the fungi.

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A colony of bread mold is actually composed of millions of tiny fungi organisms.
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Tiny fungi organisms produce sporangia which release spores, which will spread about.
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Spores from the origional colony spread to other areas and grow new colonies.


Summary:
Sporulation is an efficient method of asexual reproduction since it produces thousands of tiny spores—each of which can spread and develop into a genetically identical adult. Sporulation is important because it gives sessile organisms like bread mold the ability to disperse offspring in a manner that is typically seen only in plant seeds.
In sporulation, every spore (tiny specialized cells with the same genetic information as the mother fungus organism) has the potential to grow and become a genetically identical adult-size organism.




Vegetative Propagation:

Introduction:
Vegetative propagation involves asexual plant reproduction. It is important to remember before we begin to discuss the methods of asexual reproduction in plants that plants are an entire kingdom, and a very large one at that. Not all of the methods that are discussed here will apply to all types of plants. That being said; many plants naturally reproduce asexually by various methods. Many other plants don't naturally reproduce asexually, but can be made to reproduce by man-made methods. On this page, we will first examine a few of the ways that plants naturally reproduce asexually. Sometimes, however, gardeners and farmers want to reproduce plants that don't naturally reproduce asexually. The second part of this section will explore the methods that are often used to for these goals.

Natural methods of vegetative propagation:
Most methods of asexual reproduction seen naturally among plants make use of a specialized modified stems. Strawberry plants and spider plants, for instance, reproduce by growing a plantlet at the end of a runner. A runner is a horizontally growing stem which produces a plantlet at its end or at its nodes. Runners are fast growing and some plants have runners that can scale up buildings or across landscapes.
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here, the runners of a strawberry plant are producing plantlets.


Another method that plants use to reproduce asexually is the growth of bulbs. Bulbs are thick, fleshy leaves that are wrapped around each other to create a round mass under the surface of the soil. These thick leaves grow on a modified short stem that lies beneath the leaves. The roots of the plants grow out of this stem region. Onions and tulips are examples of plants that grow a bulb. Bulbs act as an asexual reproductive structure by allowing the plant to die back nearly entirely during the winter and then grow back in the spring.
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The bulb of an onion is technically composed of leaves. A bulb is an asexual reproductive structure for the plant.


Rhizomes are stems that grow underground like a root. Rhizomes travel underground away from a mother plant to produce daughter plants nearby. Various plants, from bamboo to water lilies reproduce asexually through the use of rhizomes. Most types of grasses produce rhizomes as a method of asexual reproduction. Rhizomes produce genetically identical plants in an area surrounding the mother plant.
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The rhizomes of this grass plant will allow it to spread throughout the area.


Artificial methods of vegetative reproduction.
Many times throughout the course of human history we have discovered plants that have beneficial aspects. When we found a plant that we wanted more of, we often gathered seeds from it and then planted these seeds elsewhere. However, seeds are the product of a plant’s sexual reproduction, and many times these seeds don’t have the exact same qualities that the mother plant did.

In times when we have wanted an exact copy of a plant, we found ways to make plants reproduce asexually. The first of these methods that we will discuss here is called taking cuttings. When we take a cutting of plant, we remove a portion of the mother plant that can be safely lost without damaging its health. This portion may be a root, stem, or leaf portion. In order to make the removed portion of the plant become a new plant, gardeners will put the plant in damp soil or water for a period. Since most plants have undifferentiated cells at key locations throughout the plant, the cut plant can use its stored sugars and starches to produce the necessary organs that it needs. Once established, the gardener can plant the newly grown plant, and it will grow into a healthy, mature plant.
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Small portions of one plant were removed. In time, these peices have grown roots. They are genetically identical to their mother plant


The second artificial method that we will explore about is called grafting. In grafting, two or more plants are creatively attached together. In time, the region between these two similar plants heals together, and the vascular system mends to create a continuous system of xylem and phloem. Once this has occurred, the foreign stem will receive nourishment and grow as if it was still growing on its own mother plant.
Grafting is used very commonly for fruiting trees. Sometimes, a fruit tree may have desirable fruit, but its root system will be poor. To resolve this issue, gardeners will choose a similar tree species that has a strong root system. They will remove most of the stems of the plant with the strong root system, and will graft on healthy stems from the fruit tree with desirable fruit.
Plants that are grafted together will not modify their own genetic information in any way, and they also won’t exchange their DNA with each other. Instead, the original portions of the plant will continue to grow and develop as their DNA instructs, and the portions of the plant that have been grafted on will grow and develop as their own DNA instructs.
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Plant stems of one plant were removed and strategically attached to a closely related plant. In this instance, the root-stock plant species will help the stems grow into strong and healthy plants.
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Stems from an apple tree with desired fruit are grafted onto the stem of an established tree as a method of producing more of the desired fruit.






Parthenogenesis

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Some species of animals can reproduce by a process called parthenogenesis. In parthenogenesis, a female organism will produce a diploid egg, which will implant and develop into a female offspring. This process is entirely asexual; no male is involved in the process at all, and the daughter will be genetically identical to her mother. The New Mexico Whiptail lizard is a species with only females. When a Whiptail lizard reproduces, she produces a diploid egg which will grow to maturity as a genetically identical female.