Asexual Reproduction Definition
Asexual reproduction is reproductive strategy for duplicating an organism’s genetic code and cellular components. There are several distinct strategies through which this can occur, but it results in more cells with the same DNA. Some organisms use both asexual reproduction and sexual reproduction. Asexual reproduction is also found throughout all the domains of life, from bacteria to complex multicellular life.
Types of Asexual Reproduction
Some organisms, all single-celled, can asexually reproduce simply through the act of dividing their cells. When this division creates two identical cells, it is referred to as binary fission. When it creates three or more new cells, it is called multiple fission. Either way, a number of bacteria and protists rely on this form of asexual reproduction to replicate their DNA.
First, the DNA and important cellular components are copied. The DNA is duplicated, and the organism divides by pinching the cell membrane in two, or growing a new cell wall. In single-celled eukaryotes, this process is known as mitosis because it also involves organizing and dividing a number of chromosomes holding the DNA. Larger, multi-celled organism also go through mitosis, but it does not immediately create a new organism. Though some multicellular forms of life are able to asexually reproduce, they do it through more complicated methods.
Plants have a special form of asexual reproduction known as vegetative propagation, though some species are more able than others at reproducing this way, it is common in many species. The process of vegetative propagation involves a piece of a plant being separated from the individual. The partial fragment, given the right conditions, can reorganize its tissues and cells to become a new plant.
The conditions must have plenty of moisture, and in commercial applications is sometimes aided by certain plant hormones. These chemicals stimulate the plant fragment to grow new stem, leaves, and roots. If the fragment is big enough, and has enough intact cells to feed itself during the transition, this form of asexual reproduction is possible in many plants. In some plants, such as potatoes, you can grow an entire plant from a small cutting. If you want to try this for yourself, place a small chunk of a potato (skin on) in some soil in a pot. Cover the pieces lightly, and regularly water the pot. In a week or so, you should have a potato plant.
Spores are produced via asexual reproduction, and are a method of broadcasting organisms into the environment or protecting them from harsh conditions. Many organisms produce spores, from bacteria to fungi, and even some plants. Spores will remain bound in a protective case until the conditions improve, or the spore is transferred to a better area.
For bacteria, this form of asexual reproduction is often separate from their main form of reproduction. It is set in motion by a deteriorating environment. The cells sense this happening, and spore formation is initiated. The bacteria replicates its DNA and packs it into small spores. The bacteria dies, releasing the spores into the environment.
Spores are also seen in fungi and plants, which release them into the environment as a sort of broadcasting asexual reproduction strategy. The spores in fungi are typically associated with sexual reproduction, but serve the same purpose. The spores find a favorable environment, and initiate the process of growing a new organism. Plants and some fungi exhibit an alternation of generations, switching between diploid and haploid stages. Some plants like ferns have a sporophyte generation releases these spores into the environment.
Fragmentation is a process for asexual reproduction seen in multicellular organisms in which an organism is divided, and grows into two or more complete organisms. The process is much different from fission, which only requires a single cell to divide. In the asexual reproduction process of fragmentation, the organism must regrow a significant portion of its body, organizing the cells and tissues into new organs. This process of asexual reproduction is seen in molds, lichens, many plants, sponges, and sea stars, among others.
Agamogenesis is a unique form of asexual reproduction. This form of asexual reproduction happens only in typically sexually reproducing organisms. That is because it is essentially sexually reproduction without sex. Instead of having a male gamete fertilize a female cell, there are two different ways this can happen.
In some reptiles, fish, amphibians, and insects this process has been observed as a method organisms use to reproduce. Typically, it is called parthenogenesis, which essentially means creating a new organism from a single parent cell. This can happen if the process of meiosis does not occur correctly, leaving an egg that is diploid. The species below in the middle of the photograph uses asexual reproduction almost exclusively. However, when it rarely does breed, it can create a hybrid with the species on its left, to form the species on the right.
Asexual Reproduction Examples
Examples in Microorganisms
Most microorganisms which infect humans reproduce via asexual reproduction, and bacteria are no exception. These small organisms are typically a natural part of the human body’s ecosystem. They live inside confined spaces and are usually harmless. That is, until they escape and are allowed to colonize a different part of the body. This is what is happening when you experience infection. The inflammation and pain you experience is your body trying to change the environment and destroy the bacterial invaders.
Examples in Animals
Only some animals use asexual reproduction. It is most commonly seen in the “lower” organisms, such as sponges and sea stars. Sponges have an ability to reproduce by budding, in which the create small bundles of tissue which are intended to break off. Other examples include sea stars, which can regenerate from small pieces. Some flatworms will regenerate into two individuals if cut in half. Many insects have this ability. This ability starts to become less common in the tetrapods, though it is still seen is some reptiles.
Examples in Plants
Most plants can be regenerated from a small sample, and some naturally reproduce this way. In agriculture, it is quite common to produce clones from cuttings. This means cutting part of a plant of, adding some hormones, and planting it in its own container. With the right application of water, light, and nutrients, the cutting will grow roots and become its own individual. This can be done in many species, though specialized laboratory techniques are required for some.
Advantages and Disadvantages of Asexual Reproduction
Asexual reproduction is great for reproducing quickly and efficiently. Bacteria are some of the fastest reproducing organisms on the planet. Further, for multicellular organisms it offers the ability to reproduce their DNA without going through the process of mating. Mating is a difficult process, requiring an individual to seek out another of the opposite gender. Then, the two organisms must exchange genetic material. Much energy and many resources must be expended to create these systems. Organisms which use asexual reproduction avoid this whole process, and simple divide off a new individual, or many.
One of the greatest disadvantages of asexual reproduction is the lack of genetic variety it introduces. Sexually reproducing animals rely on this variety to constantly evolve and adapt to their environments. Asexual reproduction typically entails creating an exact copy of the DNA. Though mutations can change this segment, the rate is so slow that beneficial mutations cannot be shared quickly.
However, most organisms have an adaptation to counter this. Many organisms also reproduce sexually, to introduce variety into their gene pools. Other organisms, like bacteria, can transfer genes horizontally to other individuals, without sexual interactions. This can happen when a bacteria dies and its genes get incorporated into another cell. It can also happen through the bacterial process of conjugation, which allows two living bacteria to exchange genes. This has been shown to help bacteria overcome antibiotic treatments.
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