What is Cloning and How Cloning was done to a Dolly Sheep ?

Microbiology, one of the Biology Topics, explores microorganisms and their effects.

Why is cloning used? What are the Advantanges of Cloning?

Cloning is the production of an exact copy of an animal by means of asexual reproduction. Any two animals which contain exactly the same genes are called ‘genetically identical’. An animal which is genetically identical to its parent is called a clone. A clone is an exact copy of its parent. The cloning of a large animal was successfully done for the first time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh (Scotland). They cloned a sheep named ‘Dolly’ from its parent sheep called Finn Dorset sheep (a female sheep) (see Figure). Dolly (the cloned sheep) was born on 5th July, 1996. Dolly sheep was the first mammal to be cloned.

The cloning of animals is a special kind of asexual reproduction method. The cloning in animals is done by the transfer of ‘nucleus’ of a cell. This happens as follows : The nucleus of a normal body cell of the animal (which we wish to clone) is transferred into an empty egg cell (whose nucleus has been removed). The newly formed egg cell is allowed to develop normally. An exact copy of the animal (or a clone) is produced.

Before we describe the cloning of Dolly sheep in detail, we should know the meaning of the term ‘ewe’. Ewe is a female sheep. The two sheep which were involved in the cloning of Dolly sheep were Finn Dorset ewe and Scottish Blackface ewe.

We can also call them female Finn Dorset sheep and female Scottish Blackface sheep. As the name suggests, the Scottish Blackface sheep has a black face. Keeping these points in mind, we will now describe the cloning of ‘Dolly’ sheep from Finn Dorset ewe.

Cloning of ‘Dolly’ Sheep

The Dolly sheep was cloned in the following way :

(i) A normal body cell was removed from the mammary gland of a female Finn Dorset sheep (which was to be cloned) (see Figure).

(ii) An unfertilised egg cell was taken from a female Scottish Blackface sheep and its nucleus (containing chromosomes) was removed, leaving the egg cell empty (having no nucleus) (see Figure).

(iii) The nucleus of normal body cell of Finn Dorset sheep was inserted into the empty egg cell of Scottish Blackface sheep. In this way a new egg cell was obtained (which had the nucleus of Finn Dorset sheep body cell).

(iv) The new egg cell was implanted in the uterus of another female Scottish Blackface sheep making it pregnant. After 148 days, this pregnant Scottish Blackface sheep gave birth to Dolly sheep (see Figure).

Though Dolly sheep was given birth by a Scottish Blackface sheep, it was found to be exactly identical to the original Finn Dorset sheep from whose cell ‘nucleus’ was taken. So, Dolly was a clone of Finn Dorset sheep whose ‘cell nucleus’ was used in developing it. All the body cells of Dolly sheep contained the same set of chromosomes having exactly the same genes as the Finn Dorset sheep cells.

So, though Dolly was given birth by a Scottish Blackface sheep but its real mother was Finn Dorset sheep. Since the nucleus from the egg cell of original Scottish Blackface sheep was removed, Dolly did not show any characteristic features of the Scottish Blackface sheep. For example, the Scottish Blackface sheep had a blackface but Dolly sheep did not have a blackface.

Dolly was a clone of Finn Dorset sheep and produced several offsprings of her own through sexual means in due course of time. Dolly had exactly the same genetic material as her real mother Finn Dorset sheep. Dolly died on 14th February 2003 due to a lung disease.

Since Dolly, the cloned sheep, who was born in 1996, cows (and pigs) have been cloned. The cloning of superior cows which give high milk yield has become possible now. If a high milk yielding cow was to be mated with a bull for reproduction, then the resulting offspring cow may or may not be of high milk yielding breed (because of intermixing of genes of the parent bull and mother cow). On the other hand, a cow which is cloned from a parent cow of high milk yield will be an identical copy of the parent cow and hence give high milk yield.

Advantages of Cloning

The technique of cloning enables us to produce exactly identical copies of domestic animals having favourable characteristics (without the risk of losing some of the beneficial genes or introducing unwanted genes through sexual reproduction methods). Cloning produces identical copies of the parent domestic animals and helps in preserving desirable features (like high milk yield or good quality wool) of the parent animal for future generations. For example :

1. a cow which gives high milk yield can be cloned to produce exactly identical cows which will give high milk yield, and
2. a sheep which gives high yield of superior quality wool can be cloned to produce exactly identical sheep which will give high yield of superior quality wool.

The cloning of mammals also has some disadvantages. Many cloned mammals die before birth or die soon after birth. Many times, the cloned mammals are found to be born with severe abnormalities.