Asexual reproductionPosted on September 4, 2018 - Last modified: September 8, 2018
La asexual reproduction occurs when an organism is capable of creating offspring without exchanging genetic information with another organism through sex.
In sexually reproducing organisms, the genomes of two parents combine to create offspring with unique genetic profiles. This is beneficial for the population because genetically diverse populations are more likely to endure survival challenges such as disease and environmental changes.
Organisms that reproduce asexually can suffer from a dangerous lack of diversity, but they can also reproduce more rapidly than organisms that reproduce sexually, and a single individual can find a new population without the need for a mate.
Some organisms that practice asexual reproduction can exchange genetic information to promote diversity using forms of horizontal gene transfer, such as bacteria that use plasmids to transmit small pieces of DNA. However, this method results in fewer unique genotypes than sexual reproduction.
Some species of plants, animals and fungi are capable of reproducing both sexually and asexually, depending on the demands of the environment.
Asexual reproduction is practiced by most single-celled organisms including bacteria, archaebacteria, and protists. It is also practiced by some plants, animals, and fungi.
Table of Contents
Advantages and disadvantages
Asexual reproduction has a series of advantages and disadvantages, now we will talk about the most important advantages and disadvantages within asexual reproduction, its utilities and its failures.
Advantages of Asexual Reproduction
The most important advantages of asexual reproduction include:
- Rapid population growth: This is especially useful for species whose survival strategy is to reproduce very quickly. Many species of bacteria, for example, can completely rebuild a population of a single mutant individual in a matter of days if most of the members are eliminated by a virus.
- No partner is needed to found a new town: This is useful for species whose members may be isolated, such as fungi that grow from spores blown by the wind, plants that depend on pollinators for sexual reproduction, and animals that inhabit environments with low population density.
- Lower investment of resources: Asexual reproduction, which can often be accomplished simply by having part of the parent organism separate and take on a life of its own, requires fewer resources than raising a new baby organism. Many plants and marine creatures, for example, can simply separate a part of themselves from the parent organism and make that part survive on its own.
Only offspring that are genetically identical to that of the parents can be produced in this way: nurturing the creation of a new organism whose tissue is different from the tissue of the parents requires more time, energy and resources.
This ability to simply split in two is one of the reasons that asexual reproduction is faster than sexual reproduction. sexual reproduction.
Disadvantages of asexual reproduction
The biggest disadvantage of asexual reproduction is the lack of diversity. Because members of a population that reproduce asexually are genetically identical except for the rare mutants, they are all susceptible to the same diseases, nutritional deficits, and other types of environmental difficulties.
The Irish Potato Famine was an example of the negative side of asexual reproduction: Irish potatoes, which had reproduced primarily through asexual reproduction, were all vulnerable when a killer plague swept the island. As a result, almost all the crops failed, and many people starved to death.
The near-extinction of the Gros-Michel banana is another example: one of the two main banana crops, it became impossible to cultivate it commercially in the XNUMXth century after the appearance of a disease to which it was genetically vulnerable.
On the other hand, many species of bacteria take advantage of their high mutation rate to create some genetic diversity while using asexual reproduction to grow their colonies very quickly. Bacteria have a higher rate of errors in the copying of genetic sequences, which sometimes leads to the creation of new useful traits even in the absence of sexual reproduction.
Types of asexual reproduction
There are many different ways to reproduce asexually. These include:
- Binary fission: This method, in which a cell simply copies its DNA and then divides in two, giving a copy of its DNA to each 'daughter cell', is used by bacteria and archaebacteria.
- Budding: Some organisms separate a small part of themselves to become a new organism. This is practiced by many plants and marine creatures, and some single-celled eukaryotes such as yeast.
- Vegetative propagation: Like the sprout, this process involves a plant growing a new sprout that is capable of developing into a completely new organism. Strawberries are an example of plants that reproduce using "runners," which grow outward from a parent plant and then become separate and independent plants.
- Sporogenesis: Sporogenesis is the production of reproductive cells, called spores, which can grow into a new organism. Spores often use strategies similar to those of seeds. But unlike seeds, spores can be created without fertilization by a sexual partner. Spores are also more likely to spread autonomously, for example through the wind, than to depend on other organisms such as animal carriers to spread.
- Fragmentation: In fragmentation, a "parent" organism splits into multiple parts, each of which grows into a complete and independent "child" organism. This process is similar to sprouting and vegetative propagation, but with some differences.
First, fragmentation cannot be voluntary on the part of the "parent" organism. Earthworms and many plants and marine creatures are capable of regenerating entire organisms from fragments after injury that divide them into multiple pieces.
When fragmentation occurs voluntarily, the same parent organism can divide into many roughly equal parts to form many offspring. This is different from the processes of budding and vegetative propagation, in which an organism develops new parts that are small compared to the parent and that are destined to become child organisms.
- Agamenogenesis: Agamenogenesis is the reproduction of normally sexual organisms without the need for fertilization. There are several ways this can happen.
In parthenogenesis, an unfertilized egg begins to develop into a new organism, which by necessity only possesses genes from its mother. This occurs in a few fully female animal species, and in the females of some animal species when no males are present to fertilize the eggs.
In apomoxis, a plant that normally reproduces sexually reproduces asexually, producing offspring identical to the mother plant, due to the lack of availability of a male plant to fertilize the female gametes.
In the nucellar embryo, an embryo is formed from the parents' own tissue without meiosis or the use of reproductive cells. This is known to occur mainly in citrus fruits, which can produce seeds in this way in the absence of male fertilization.
One might think that the ability to reproduce without a sexual partner is relegated to the world of plants, fungi, and single-celled organisms. But some animals, such as those that walk, swim, and fly, can reproduce without a partner. This process, called asexual reproduction, is not necessarily common, but it is helpful for some animals that may have trouble finding a reproductive partner.
The marbled crab or Marmorkrebs, resembling tusked shrimp, they are an asexual form of crawfish that live in Florida and southern Georgia, but don't belong there.
The marmorkreb, whose name means "marbled crab" in German, is an invasive species that has established populations in three countries while greatly disrupting native wildlife.
Many jurisdictions regulate the importation and release of various types of crayfish. In 2011, Missouri added marbles to its list of prohibited species. Marmorkrebs achieve asexual reproduction through apomixis, a process normally reserved for plants in which an organism can generate an embryo without fertilization.
While most species of asexual animals have a choice and only resort to asexual reproduction when necessary, the whiptail lizard belongs exclusively to the girls' club. This celibate, fully female species begins the reproductive process with twice as many chromosomes as its sexually reproducing relatives. Collembola evolved from hybrids of other species and can possess two complete sets of chromosomes.
Collembola live in the Southwest, Mexico and South America and are the only known unisexual reptiles.
Despite some pretty compelling reasons why komodos don't make great pets, including that their saliva is usually toxic, some people keep these giant lizards around the house.
Worries aside, female komodos have a unique ability to lay eggs without ever having sex, and these eggs will produce healthy male offspring. This occurs because female komodos have two different sex chromosomes, W and Z, that multiply on their own in the ovules.
These eggs develop into unviable WW females or ZZ males, assuming that in an isolated environment the female will create males to mate with and presumably produce more female komodos.
Sharks in captivity
Although they are not strictly pets, captive sharks have reproduced asexually, if only on rare occasions.
Female hammerhead fish caught as hatchlings and kept away from males in Florida were the first to do this, and the discovery left mammals as the only vertebrates unable to give birth by parthenogenesis or without sexual contact.
The tiny and humble hydra is a favorite subject of scientists because it has an enviable and almost unique trait: it shows no signs of aging. It also offers scientists an uncontroversial way to investigate beneficial human stem cells.
But hydras have another unusual trait in that they can choose to reproduce sexually or asexually. When food is abundant, hydras reproduce by themselves; But when food becomes scarce, they mate with their sexual partners to generate more diversity in species.
Cloning of Wasps
Asexual reproduction of wasps is complicated. When certain species become infected with the Wolbachia bacteria, the chromosomes in the wasp eggs change. As a result, the eggs do not divide, and instead of creating unique offspring, wasp mothers create female clones of themselves.
It sounds like a survival trick, but the wasps are only buying time. Eventually the bacteria create only female clones that are infected.