When bacteria reproduce asexually, they transmit their genetic material, and the cell divides equally to form a genetically identical population. These are known as natural clones.

The process of producing genetically identical copies of cells is termed as cloning. Similarly, many unicellular organisms, including yeast, reproduce by natural cloning. The identical population is characterized by the absence of genetic alterations and recombination.

Based on this natural principle, with the advent of recombinant DNA technology, scientists created artificial clones.

In the 1970s, cloning experiments were started in animals, where the first sheep was produced from differentiated embryonic cells.

In 1996, British Scientist named Ian Wilmut generated the first animal cloned from the somatic cell nuclear transfer method (SCNT). The cloned sheep was named as Dolly. This discovery was a breakthrough in the field of science, which produced a complete genetically identical sheep.

In addition, this method also helped in discovering a novel principle of reprogramming of somatic cells into a pluripotent state, where somatic cells were skewed into embryonic states which were capable of differentiating into different cell types. Thus it has paved the way for stem cell therapies.

Generation Of Animal Clones – Dolly
The donor is an animal whose genetic material is copied. Firstly the nucleus was extracted from an udder cell of a six-year-old Finn Dorset white sheep. This sheep is often referred to as Donor sheep. The nucleus contains all the genes required to produce offspring and was grown in a growth media.

Secondly, another sheep was selected from which the nucleus was removed, but an unfertilized egg cell was extracted. The nucleus from the first sheep was then introduced into the egg cell of the second sheep.

The egg cell containing the genetic material of the mother was grown in a test tube for six to seven days until it reached the embryonic stage. Next, the embryo was transferred into another sheep (Scottish blackface ewe), referred to as a surrogate mother.

The implanted embryo, after completing its gestation and birth, contained the exact genetic copy and identity of donor sheep from where the nucleus was extracted. This clone was named Dolly.

The reports revealed that from 277 cell fusions, only 29 embryos could develop, which were further implanted into 13 surrogate mothers. Of 13, only one pregnancy attained full-term and developed into Finn Dorset lamb Dolly.

Dolly grew, mated, and delivered a lamb just like natural sheep.

After Dolly, several animal clones were generated based on this principle, such as pigs, goats, rats, mice, dogs, horses, and mules. But some of these animals had problems in their survival, and after several advances in the methods, live birth of two macaques was successful by SCNT.

Applications Of Animal Clones
Due to ethical reasons involved in cloning human beings, the cloned animals are raised mostly for therapeutic purposes.

This method is intended to clone large animals only to raise medicinal products such as blood clotting factors IX and alpha-1-antitrypsin to treat hemophilia and cystic fibrosis, respectively.

They are used to develop human antibodies against infectious diseases and cancers.

The method is used to express proteins from foreign genes that are transplanted in zebrafishes. These fishes have significance over other animals because of their homology to human genome, easy monitoring, and shorter life cycle.

Their application has also begun in organ development, where the animal tissues from cloned animals can be used for organ transplantation (xenotransplantation). Cloned pigs have majorly tested animals for this purpose.

Cloned animals can also serve as a model organism for research applications. For instance, mice can be cloned to become obese, which in turn can lead to an understanding of the progression of the disease.

Through cloning, one can ensure the enrichment of rare breeds and the preservation of endangered species. In China, Panda cells are kept on reserve because they are on the list of extinction.

Cloned animals offer great benefits in the field of agriculture and farming, where healthy and safe foods can be produced, and agriculture products generated by the use of growth hormones, chemicals, and antibiotics can be minimized.

In 2008, FDA reaffirmed the safety of food products such as meat and milk from cloned animals, and their offspring are safe for human consumption.

Cleavage: Cleavage, a sequence of consecutive cell divisions, accomplishes the mission of the growth of the several cells that must be generated from the single-celled zygote. Blastomeres are cells manufactured during cleavage. Each chromosome in the nucleus divides into two daughter chromosomes so that the two daughter blastomeres maintain the diploid number of chromosomes. The divisions are mitotic and almost no growth occurs during successive divisions. The total volume of living matter does not change substantially as a result, the size of the cells at each division is decreased by almost half. Cell divisions appear to occur concurrently in all blastomeres at the beginning of the cleavage, and the number of cells at each division is doubled. The cells no longer divide at the same time, as cleavage progresses. Cleavage follows an ordered pattern in most species, with the first division being in the plane of the egg’s principal axis. The cleavage plane is considered vertical. Once again the second cleavage plane is vertical but at right angles to the first, resulting in four equal cells grouped around the egg’s main axis. The third cleavage plane is horizontal, or equatorial, at the right angle of both the first and second cleavage planes. Between vertical and horizontal cleavage planes, subsequent divisions can alternate, but later cleavage divisions become randomly oriented. This pattern is characteristic of many groups of species, but in animals such as annelids, mollusks, and nematodes, more complex cleavage patterns are found. The blastula formation signifies the end of the cleavage phase. The next stage of growth is not an increase in the number of cells, while cell divisions proceed at a slower rate, but a rearrangement of the cell masses required to conform to the gross characteristics of the future species. Before it can enter the adult organization, the embryo in the blastula stage must go through profound transformations. Usually, an adult multicellular animal has a concentric arrangement of the body’s tissues; this characteristic is common to all classes of animals above the level of sponges. Three embryonic cell layers are derived from adult tissues, called germinal layers: the ectoderm is the outer layer, the mesoderm is the middle layer, and the endoderm (entoderm) is the innermost layer. The endoderm lines the food canal and gives rise to digestive and breathing-related organs in chordates.