A zygote is diploid cell, which means that it has twice the number of chromosomesas a gamete. Cycle of Sexual Reproduction. Sexual reproduction involves the production of haploid gametes by meiosis. This is followed by fertilization and the formation of a diploid zygote.
The number of chromosomes in a gamete is represented by the letter n. Why does the zygote have 2n, or twice as many, chromosomes? Reproduction: Asexual vs. Sexual Cell division is how organisms grow and repair themselves. Asexual Reproduction Asexual reproduction involves a single parent. Binary fission occurs when a parent cell splits into two identical daughter cells of the same size. Fragmentation occurs when a parent organism breaks into fragments, or pieces, and each fragment develops into a new organism.
Starfish, like the one in Figure below , reproduce this way. A new starfish can develop from a single ray, or arm. Starfish, however, are also capable of sexual reproduction. Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops.
When the bud is fully developed, it breaks away from the parent cell and forms a new organism. Budding in yeast is shown in Figure below. Sexual Reproduction Sexual reproduction involves two parents. Summary Asexual reproduction involves one parent and produces offspring that are genetically identical to each other and to the parent.
Sexual reproduction involves two parents and produces offspring that are genetically unique. During sexual reproduction, two haploid gametes join in the process of fertilization to produce a diploid zygote. Meiosis is the type of cell division that produces gametes. Explore More Use this resource to answer the questions that follow.
Sexual vs. How do the offspring of asexual reproduction compare to the parent? This process occurs, for example, in many asteroid echinoderms through splitting of the central disk.
Some sea anemones and some coral polyps Figure 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 and breaks away from the main body, as illustrated in Figure Watch a video of a hydra budding. 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 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.
Parthenogenesis 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.
Sexual reproduction is the combination of usually haploid reproductive cells from two individuals to form a third usually diploid unique offspring. Sexual reproduction produces offspring with novel combinations of genes. This can be an adaptive advantage in unstable or unpredictable environments.
Vegetative reproduction results in new plant individuals without the production of seeds or spores. Many different types of roots exhibit vegetative reproduction. The corm is used by gladiolus and garlic. Bulbs, such as a scaly bulb in lilies and a tunicate bulb in daffodils, are other common examples of this type of reproduction.
A potato is a stem tuber, while parsnip propagates from a taproot. Ginger and iris produce rhizomes, while ivy uses an adventitious root a root arising from a plant part other than the main or primary root , and the strawberry plant has a stolon, which is also called a runner.
Roots : Different types of stems allow for asexual reproduction. Both corms and bulbs can self-propagate, giving rise to new plants. Each eye in the stem tuber can give rise to a new plant. Some plants can produce seeds without fertilization. Either the ovule or part of the ovary, which is diploid in nature, gives rise to a new seed.
This method of reproduction is known as apomixis. An advantage of asexual reproduction is that the resulting plant will reach maturity faster. Since the new plant is arising from an adult plant or plant parts, it will also be sturdier than a seedling. Asexual reproduction can take place by natural or artificial assisted by humans means. Plants can undergo natural methods of asexual reproduction, performed by the plant itself, or artificial methods, aided by humans.
Natural methods of asexual reproduction include strategies that plants have developed to self-propagate. Many plants, such as ginger, onion, gladioli, and dahlia, continue to grow from buds that are present on the surface of the stem.
In some plants, such as the sweet potato, adventitious roots or runners stolons can give rise to new plants. In Bryophyllum and kalanchoe, the leaves have small buds on their margins. When these are detached from the plant, they grow into independent plants; they may also start growing into independent plants if the leaf touches the soil. Some plants can be propagated through cuttings alone. Runners: asexual reproduction : A stolon, or runner, is a stem that runs along the ground.
At the nodes, it forms adventitious roots and buds that grow into a new plant. Artificial methods of asexual reproduction are frequently employed to give rise to new, and sometimes novel, plants. They include grafting, cutting, layering, and micropropagation. Grafting has long been used to produce novel varieties of roses, citrus species, and other plants. In grafting, two plant species are used: part of the stem of the desirable plant is grafted onto a rooted plant called the stock.
The part that is grafted or attached is called the scion. Both are cut at an oblique angle any angle other than a right angle , placed in close contact with each other, and are then held together. Matching up these two surfaces as closely as possible is extremely important because these will be holding the plant together. The vascular systems of the two plants grow and fuse, forming a graft.
After a period of time, the scion starts producing shoots, eventually bearing flowers and fruits. Grafting is widely used in viticulture grape growing and the citrus industry. Scions capable of producing a particular fruit variety are grafted onto root stock with specific resistance to disease. Grafting : Grafting is an artificial method of asexual reproduction used to produce plants combining favorable stem characteristics with favorable root characteristics.
The stem of the plant to be grafted is known as the scion, and the root is called the stock. Plants such as coleus and money plant are propagated through stem cuttings where a portion of the stem containing nodes and internodes is placed in moist soil and allowed to root. In some species, stems can start producing a root even when placed only in water. For example, leaves of the African violet will root if kept undisturbed in water for several weeks.
Layering is a method in which a stem attached to the plant is bent and covered with soil. Young stems that can be bent easily without any injury are the preferred plant for this method. Jasmine and bougainvillea paper flower can be propagated this way.
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