Asexual Reproduction:

In this type of reproduction neither the sex cells (nor gametes) are formed nor do they unite to form the zygote. Moreover, the participation of two organisms (male and female) is not required, only one organism reproduces. During asexual reproduction the body (somatic) cells divide, their nucleus divides either by mitosis or amitosis, therefore, such type of reproduction is also known as somatogenic or blastogenic reproduction. The asexual reproduction is commonly found in lower animals such as protozoans, sponges, coelenterates, certain worms and tunicates.

Principal forms of asexual reproduction are:

1. Binary fission

2. Budding

5. Fragmentation

1. Binary Fission:

This is the simplest and most common method of asexual reproduction seen in unicellular organisms. This occurs under the favourable conditions of the environment. After the organism grown to its full size, the parent divides into two daughter cells which are genetically and morphologically similar. During this process, the nucleus divides into two, followed by the division of the cytoplasm.

2. Budding:

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, which breaks away from the main body; whereas in coral budding, the bud does not detach and multiplies as part of a new colony.

 

3. Fragmentation:

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.

Many sea stars reproduce asexually by fragmentation. For example, if the arm of an individual sea star is broken off it will regenerate a new sea star . Fishery workers have been known to try to kill the sea stars that eat 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.