The process of creating a whole new individual from already existing individuals is known as reproduction. It is a wonderful process which maintains continuity of every living organism in the world. There are two methods of reproduction in living organisms - sexual and asexual reproduction.
Since human beings reproduce sexually, most people are aware of how sexual reproduction takes place. It requires two individuals to reproduce sexually and the young one born is a separate identity and is genetically a combination of the parents. On the other hand, asexual reproduction involves reproduction from a single parent and the young one produced is genetically similar to the parent. Plants reproduce asexually and so do certain types of animals.
Asexual Reproduction Definition
When a reproduction process does not involve any meiosis, fertilization or syngamy, it is considered to be vegetative or asexual reproduction. As there is no syngamy necessary, this process takes place in the gametophyte stage in the life cycle. The new organism formed through this is genetically identical to the parent, as there is no other genetics involved. This form of reproduction is common among single cell organisms and also plants and fungi, while multicellular organisms generally undergo sexual reproduction. Binary fission, budding, spore formation, vegetative reproduction, fragmentation, agamogenesis, parthenogenesis and apomixis are various types.
Asexual Reproduction in Plants
It can occur in plants through either budding, vegetative reproduction, fragmentation, parthenogenesis or apomixis. When certain parts of a plant get separated from the original plant, new plants grow from this and the process is called fragmentation. Budding causes cells to divide into two - parent and daughter cell. As the daughter cell develops completely, it separates itself from the parent and develops individually. The Hydra plant shows this process. Parthenogenisis is a form of asexual reproduction where in an unfertilized egg transforms into a new individual all together. Few plants have the ability to produce seeds, in spite of flowers being undeveloped. This is known as apomixis. In this process, the diploid cell in the ovule creates a new embryo. This eventually develops into a seed. An example of this process is found in dandelion.
Asexual Reproduction in Animals
Very few species of animals reproduce asexually, as most of them are multicellular. Jellyfish and echinoderms reproduce asexually through the process of budding. Young ones grow on the parent body and then detach themselves when fully developed. Few worms, on developing completely, automatically degenerate into pieces. Every such fragment matures into a full sized worm and the process is repeated when it grows completely. This process is known as fragmentation. When the female organism lays eggs and they develop into an offspring without any fertilization, it is called parthenogenisis. Few insects, fish and frogs reproduce this way.
All prokaryotic organisms and a few eukaryotic organisms reproduce asexually through binary fission. The binary fission process starts when the cell produces two sets of matching DNA within itself. It then grows to a larger size. During this growth period, both DNA sets get separated and place themselves one at each end of the cell. When the cell has fully grown, it divides into two cells, thereby producing two daughter cells with matching DNA. Binary fission works when an organism is staying in a stable environment. Examples include - fungi, bacteria and protists.
Why is Mitosis a Form of Asexual Reproduction?
Mitosis is a process similar to binary fission in which cells split into two and more number of identical cells. Since the process does not require two organisms (male and female) and the new organisms produced are genetically similar to the parent cell, mitosis is a form of asexual reproduction. The human skin cells are a good example of mitosis.
This type of reproduction can be beneficial for certain animals. Especially those staying at a particular place and cannot find mates to reproduce sexually. Other than this, an offspring generated through asexual reproduction saves the parent a lot of time and energy, which sexually reproductive organisms spend. Stable and non-changing environment are most suitable for asexual reproduction.
A disadvantage is the fact that the offspring is a clone of the parent. There is no difference at all and this may hinder their evolution process. Another factor against asexually reproduced organisms is their inability to adapt to changing environment. This has brought a few species close to extinction.