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Asexual Reproduction in Animals

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Asexual Reproduction in Animals - Lesson Summary

Reproduction
Reproduction is the biological process by which existing organisms give rise to their offspring. Reproduction can be of two types – Sexual mode and Asexual mode.



Asexual mode of reproduction
This is a type of reproduction which involves single parent in giving rise to offspring. Animals reproduce asexually by different processes like binary fission, budding, fragmentation, regeneration, cloning etc.



Binary fission: It involves the longitudinal or transverse splitting of an organism into two equal halves which develop into two separate individuals.



       •  Binary fission is generally seen in unicellular organisms such as amoeba and paramecium falling into the category of protozoa. Amoeba is a simple, unicellular organism which reproduces by binary fission. The division begins with the division of nucleus.
       •  Binary fission can also be observed in multicellular animals like sea anemones and planarians.




Budding: This is a form of asexual reproduction which involves development of small mass of cells as protuberances on the parental body to give rise to new structures called as buds. These buds separate out from the parental body and develop into new individuals. Two types of budding are external budding and internal budding.



       •  External budding involves the bud to act as an individual before separation from the parent. e.g. Sponges, coelenterates, flatworms and tunicates.
       •  Internal budding involves the bud to transform into different form not resembling a parent after separating itself from the parent. e.g. Obelia, a coelenterate gives rise to medusa.

Fragmentation: It involves breaking of parent organism into two or many fragments. Each fragment develops into an individual organism. Fragmentation is seen in sea stars which accidentally break their body into fragments. Fragmentation is also observed in annelids, turbellarians and some of poriferans.



Regeneration: It is one type of fission which involves division of parent into number of parts, each of which is capable of regenerating the missing parts to form a complete organism. Regeneration can be seen in flat worms, ribbon worms and some annelids.



Cloning: It involves the creation of an exact copy of a biological entity.
       •  Cloning involves the process of forming  a cell or a complete individual from a body cell.
       •  A clone is created by inserting the complete genetic material of a regular body cell from a donor into a recipient.
       •  Cloning is done in many animals including sheep, cattle, pigs etc. But for the first time cloning of sheep was successful in producing a clone of the parent sheep.

Cloning in sheep
Dolly was the first cloned mammal, and is genetically identical to its parent sheep.
       •  Sir Ian Wilmut from Roslin Institute in Edinburgh, Scotland created Dolly.
       •  Egg from A was taken and enucleated.
       •  Nucleus of a body cell was selected from B and was injected into enucleated cell of A.
       •  This new cell of A with nucleus from B is placed into womb of A.
       •  It developed into a normal baby sheep which was named as Dolly.
       •  Dolly was found to be exactly similar to B from which nucleus was taken.
       •  Dolly was termed to be a 'Clone' and the process was referred to as 'Cloning'.
       •  Dolly was developed from the cell of A and in the womb of A. But she resembled B which donated the nucleus.
       •  Cloning involves certain abnormalities. Dolly suffered from arthritis. Dolly also was suspected to have developed lung tumour.

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