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Asexual Reproduction

A short paper on the different types of Asexual Reproduction.

Asexual reproduction

 

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Binary Fission

Binary fission is the most common mode of cell division. It is the division of a cell into two separate and similar parts which then have the potential to grow to the same size of the original. For example: In bacteria, the chromosome replicates and then divides in two, after which a cell wall forms across the elongated parent cell and In higher organisms, there is first duplication and then a separation of the chromosomes (mitosis), after which the cytoplasm divides in two. In the wall cells of higher plants, a median plate forms and divides the mother cell into two compartments.

Budding

Budding is a form of asexual reproduction in which a new individual develops from some point of the parent organisms’ body. In some species buds may be produced from almost any point of the body, but in many cases budding is restricted to specialized areas. The initial increase of cytoplasm or cells  and the bud, eventually develops into an organism duplicating the parent. The new individual may separate to exist independently, or the buds may remain attached, forming aggregates or colonies. Budding is characteristic of a few unicellular organisms (some bacteria, yeasts, and protozoans).

Vegetative Reproduction

Vegetative reproduction involves but one parent being needed to create another individual instead of two. Many home gardeners are familiar with vegetative reproduction and practice it without necessarily knowing it by that name. A very common example is the growing of a new plant from a cutting. Similarly, many gardeners are familiar with the dividing of plants. A gardener who divides a plant to get two where there was previously one is again propagating vegetatively. Non-vascular plants can reproduce vegetatively in various ways. Vegetative reproduction is known from bryophytes where sexual reproduction has never been seen.

Fragmentation

Fragmentation involves the production of new tissue and is normally responsible for replacing damaged and lost parts of some highly developed invertebrate animals. In some of these animals, entirely new individuals can be created from separated body parts. For example, the starfish can regenerate an entirely new individual from a single arm providing that part of the central disc is present. In some species of aquatic worm, the ability to regenerate body parts has turned into a means of reproduction. These worms just break up into different parts, which each grow the missing parts back to form complete worms.

Parthenogenesis

Parthenogenesis is a form of asexual reproduction in which egg cells develop into embryos without fertilization. In some species of aphids, females produce eggs during spring and summer that “parthenogenetically” develop into new offspring. A female might have up to 10 parthenogenetic cycles in a season, producing from three to one-hundred offspring per cycle. The offspring mature to the parents’ age within a few days and may also start producing eggs. In good conditions, the population numbers can explode very easily. Most of the offspring are female but some are winged males, which can then fly to a different plant, mate with a female and produce fertilized eggs.

 

Spore formation

Many organisms form spores during their life in a process called sporogenesis. Exept for animals and some protists, who undergo gametic meiosis straight away followed by fertilization. Plants and many algae undergo sporic meiosis where meiosis leads to forming haploid spores rather than gametes. Haploid spores grow into other individuals, called gametophytes, without fertilization. These individuals produce gametes through mitosis. Meiosis and gamete formation happens in separate generations of the life cycle. Sexual reproduction is often defined as the fusion of gametes (fertilization), spore formation in plants might be considered a form of asexual reproduction (agamogenesis) even though it is the result of meiosis. However, both spore formation and fertilization are necessary to complete sexual reproduction in the plant life cycle.

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