Modes of Reproduction
Organisms, which include animals and plants reproduce as a law of nature, a means of ensuring the survival of the species and in the context of evolution. They must choose among different methods to do so. There are two major classifications, sexual and asexual reproductions. Each has its own advantages and disadvantages and each is appropriate for different species. Vertebrates, such as humans, are almost exclusively sexual in their reproduction. Many simpler animals are asexual. It is important to understand how these processes differ.
Asexual reproduction spans a variety of methods. The simplest one-celled organisms may reproduce by binary fission. In the process, the cells simply divide in half creating a clone of the parent and holds the benefit of usually being very quick and energy efficient. For example, bacteria that reproduce by binary fission can give rise to progeny every few hours. Multiple fission also exists in which they split into more than one offspring. Organisms such as Cryptosporidium parvum, sporozoan, etc may utilize multiple fission.
While in multicellular organisms, a similar method is named fragmentation in which small pieces break off and grow into new organisms. Another method involves budding, which may lead to the production of a completely new adult that forms away from the original body or may remain attached to the original body. A common thread in all this is that the offspring is a direct clone of the parent. The purpose of reproduction as we’re well aware is to propagate one’s own genes. Evolutionarily, asexual reproduction is a good bet for the species. It is quick, simple and the genes of the parent will not be diluted by those of another individual. Also, an organism that reproduces asexually can reproduce about twice as fast as one that reproduces sexually.
Sexual reproduction is the combination of reproductive cells from two individuals to form a third unique offspring. Sexual reproduction produces offspring with a different combination of genes. This could turn out to be an adaptive advantage in an unpredictable environment and plays an important role in evolution.
One must understand that the sexual reproduction is a lot more complex than asexual reproduction. It includes the production of gametes, which have half the number of chromosomes of all other cells in the organism and the process of meiosis, which produces haploid cells from diploid cells which could lead to the possibility of two copies of a single chromosome crossing over to create a completely new chromosome that contains a new combination of genes. You see, switching from chromosome to chromosome is a good way to ensure that the genes will keep active in a given population.
|Asexual Reproduction||Sexual Reproduction|
|Only one parent is required.||Two parents are needed. They mate and produce the offspring.|
|Regeneration, fission and budding are some of the process through which cells divide.||Meiosis is the process by which the cells divide.|
|The offspring will also have a genetic disease if the parents have it i.e. no variation. This is its disadvantage.||Two organisms and a lot more energy is required. These are its disadvantage.|
|Spore formation, budding, vegetative reproduction, fragmentation are some of the types.||Conjugation and Syngamy are some of the types.|
|The advantage of this method is time efficiency, and requires less energy.||The advantage of this method is variation which produces unique organisms|
|Chance of variation is less. Mutation is less frequent.||Genetic variation takes place in every new organism. Leads to evolution|
|Sex cell or gametes are not formed.||Sex cell or gamete formation occurs|
|Lower organisms make use of this method||Higher vertebrates and invertebrates use this method|
|The unit of reproduction can be the whole parent body or a single somatic cell||Unit of reproduction is a gamete|
|The time taken is short for this type of reproduction.||This form of reproduction can take numerous months.|
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