The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Asexual and sexual reproduction, two methods of reproduction among animals, produce offspring that are clones or genetically unique.
Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. This type of reproduction occurs in prokaryotic microorganisms bacteria and in some eukaryotic single-celled and multi-celled organisms.
Animals may reproduce asexually through fission, budding, fragmentation, or parthenogenesis. Fission, 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, forming 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 also reproduce through fission. Fission : Coral polyps reproduce asexually by fission, where an organism splits into two separate organisms. Budding 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, which breaks away from the main body; whereas in coral budding, the bud does not detach and multiplies as part of a new colony. Budding : Hydra reproduce asexually through budding, where a bud forms that develops into an adult and breaks away from the main body.
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. Many sea stars reproduce asexually by fragmentation. For example, if the arm of an individual sea star is broken off it will regenerate a new sea star.
Fishery workers have been known to try to kill the sea stars that eat 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. Fragmentation : Sea stars can reproduce through fragmentation.
The large arm, a fragment from another sea star, is developing into a new individual. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly.
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. Fission , 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.
In binary fission , the cell divides to give rise to two daughter cells of equal unilateral growth. The parent basically splits into two cells with the same size. In budding, a new cell grows from an old cell. The new cell tends to be smaller than the old one. The same principle applies to single-celled eukaryotes. In fungi, such as the yeast, Saccharomyces cerevisiae , a smaller daughter cell grows on the larger mother cell.
The bud forms and stays for a while, and then detaches to grow fully as a new individual. Budding also occurs in certain invertebrates, e. Hydra sponge , corals , echinoderm larvae, and some acoel flatworms. The bud breaks off to become a new individual Hydra. Budding in plants is a form of vegetative reproduction. It occurs naturally. However, it can also be induced artificially, by horticulture. By repeating this process, budding produces what appears to be chains of yeast cells. This is referred to as the pseudomycelium and consists of loosely joined cells that break away easily over time.
Bacteria are microscopic, unicellular organisms that can be found in a variety of environments aquatic, terrestrial, human gut, etc across the world. Unlike many organisms on earth, bacteria have a simple internal structure lacking a membrane-bound nucleus.
They are classified as prokaryotes. There are many types of bacteria that are classified on the basis of nutrition, general morphology, as well as where they are found. Although binary fission is the usual mode of reproduction, some of the species reproduce through budding and are known as budding bacteria. In some bacteria species, the budding process starts with de novo wall synthesis at given points of the parent cell. Normally, this occurs at one end pole of the bacteria. De novo synthesis in the wall is an important step in the budding process which ensures that the new individual daughter cell does not use the cell envelope material of the parent.
This is then followed by DNA replication and ultimately separation of the mother and daughter cells in what is known as bacterial budding cycle. In stalked bacteria, such as Hyphomonas neptunium, this process has been shown to occur through the stalk which acts as the reproductive organelle. Through cytokinesis division of the cytoplasm during cell division to produce two new daughter cells , these cells give rise to stalked cells non-motile and swarmer cells which are flagellated and capable of swimming.
While the stalked cells are capable of entering the budding cycle, swarmers have to differentiate into stalked cells before they can go through this process. This results in the formation of a stalk on which the bud is produced.
As is the case with yeast, the bud starts growing and is ultimately separated from the parent cell to become an independent individual capable of budding. Being a prokaryote, H. It's replicated once per cell cycle in two main steps during the budding process. Here, the first step involves moving one of the duplicated centromere-like region to the stalked pole of the mother cell. This region remains at this site until the bud starts to form. This region centromere-like region is then transported at the flagellated pole through the stalk where the bud is forming.
The bud then continues growing in size before being separated from the parent cell. Based on earlier studies, budding was divided into several categories based on the cells produced through the budding process. This is commonly observed in Rhodomicrobium and Pedomicrobium. Hydra is a genus that consists of fresh-water organisms under the phylum Cnidaria. As such, they are related to such organisms as jellyfish and anemones that fall under the same phylum.
As compared to many other organisms, hydra have generated a lot of attention from the scientific community due to their regenerative ability that prevents them from aging from undergoing senescence. For these organisms, budding is the main mode of reproduction and results in the production of a new individual that resembles the parent. Based on research studies, a number of discoveries have been made with regard to the budding process in hydra.
0コメント