In this method a single parent produces offspring without the involvement of sex cells and gametes which are identical to each other and are also similar to their parents. This process is very common in unicellular organism and is said to be the simplest type of reproduction
Example – Binary fission in Amoeba, budding in hydra, spore formation in rhizopus, fungus and vegetative propagation in flowering plants like rose, etc.
Characteristics of asexual reproduction.
• It is a rapid mode of multiplication
• Cell division takes place either mitotically or amitotically.
• The new individual produced after cell division are always genetically identical to the parents that is clone
• A single parent is involved that is opposite sex and not involve
• It does not involve the fusion of gametes.
The mode by which various organisms reproduce depend on the body design of the organism.
1) Fission – It is defined as the splitting of a unicellular organism into two or more than two separate daughter cells. It is the most common and simplest method of a sexual reproduction in unicellular organism such as bacteria and protozoa. It is a division of an organism into two or more part during cell division, which develop into whole new organism. Fusions are of two types.
a) Binary Fission – In this method parent organism divides into two identical daughter organism which definite orientation. At first the nucleus divide automatically into two followed by the division of the cytoplasm and finally to the splitting of parent all into two daughter cell. Binary fission can be seen in organisms such as Amoeba and paramecium, euglena, etc.
b) Multiple Fission – In this method parent organism divide into many identical daughter organism. The nucleus of the cell splits rapidly to form many smaller nuclei which called daughter nuclei surrounded by a little bit of cytoplasm and thin membrane around them. New daughter cells are formed from a single parent cell within the cyst and in the favourable conditions. The cyst burst and the daughter cells are released each forming a new organism. Multiple fussion can be seen in organisms such as plasmodium, monocytes, etc.
2) Fragmentation – It is a form of asexual reproduction in which multicellular organism like filamentous algae which break up into two or more small fragments or pieces. on maturing each of which subsequently grows to form a complete new organism. Multicellular organism cannot divide cell by cell and therefore need of complex way of reproduction.
3) Regeneration – Many organisms like Hydra and planaria can be renewed into a complex individual from a single segment. That is a fully differentiated organism which can give rise to individual organism from his body parts. This growth of whole new organism from just broken or cut part is termed as regeneration. Regeneration is carried out by specialised cells which proliferate and make large number of cells. From this mass of cells, different cells undergo changes to become various cell types. These changes take place in an organised sequence known as development.
4) Budding – In budding a daughter organisms is formed from a small projection known as bud, which develop as an outgrowth. Due to repeated cell division on the parent body and later detaches to grow into a new independent division. Hydra is a multicellular organism uses regenerative cells for production in the process of budding.
5) Spore formation – In many multicellular organism, sporongia like structures are the reproductive organ which contains spores. Living cell of spore have the ability to germinate and give rise to a new colony. This type of reproduction occur in bacteria, algae, fungi, Ferns and mosses. Example in rhizopus thread like projection called hyphae if a moist bread is kept for a few days as a source of rhizopus present in the air settle down on the bread and germinate to form a new colony. The spores are covered by thick wall that protect them until they can into contact with some more surface like soil and can begin to grow.