Cloning In Animals

What is cloning a natural part of?

The reproductive cycle in many plants.

Where is natural cloning common?

In invertebrate animals. Although it is less common in vertebrates, it still occurs in the form of twinning.

What are the different forms in which cloning in invertebrates can take place?

Some animals, such as starfish, can regenerate entire animals from fragments of the original if they are damaged. Flatworms and sponges fragment and form new identical animals as part of their normal reproductive process, all clones of the original. Hydra produce small buds on the side of their body which develop into genetically identical cones. In some insects, females can produce offspring without mating.

What is the main form of vertebrate cloning?

The formation of monozygotic (identical) twins. The early embryo splits to form two separate embryos. No one is sure of the trigger which causes this to happen.

What does the frequency at which identical twins occur vary between?

Species.

When monozygotic twins are botn, although they are gentically identical, why might they look different?

As a result of differences in their position and nutrition in the nucleus.

What can some female amphibians and reptiles produce?

Offspring, when no male is available. Their offspring are often male rather than female, so they are not clones of their mother, yet all of their genetic material arises from her.

Is it difficult to produce artificial clones of some invertebrates?

Yes.

Is it difficult to produce artificial clones of vertebrates?

Yes, especially mammals. However, two methods are now widely used in the production of high-quality farm animals and in the development of genetically engineered animals for pharming.

After an egg is fertilised, what does it divide to form?

A ball of cells, and each of these individual cells is totipotent - it has the potential to form an entire new animal. As the cells continue to divide, the embryo becomes a hollow ball of cells. Soon after this, the embryo can no longer divide successfully.

What happens in natural twinning?

An early embryo splits, and two foetuses go on to develop the same two halves of the divided embryo.

What happens in artificial twinning?

The same as in natural twinning, but the split in the early embryo is produced manually. In fact, the early embryp may be split into more than two pieces and result in a number of identical offspring.

Who is artificial twinning used by?

The farming community, to produce the maximum offspring from particularly good dairy or beef cattle or sheep.

What is the first stage in the artificial twinning of cattle?

A cow with desireable traits is treated with hormones so she super-ovulates, releasing more mature ova than normal.

What happens to the ova produced from the cow with desireable traits?

They may be fertilised naturally, or by artificial insemination, by a bull with particularly good traits. The early embryos are gently flushed out of the uterus.

Alternatively, how are the ova from the cow with desireable traits fertilised?

They are removed and then fertilised by top-quality bull semen in the lab.

What happens after the ova are fertilised?

Usually before or around day 6, when the cells are still totipotent, the cells of the early embryo are split to produce several smaller embryos, each capable of growing to form a healthy full-term cell.

What happens to the split embryos?

Each of the split embryos is grown in the lab for a few days to ensure all is well before it is implanted into a surrogate mother. Each embryo is implanted into a different mother, as single pregnancies carry fewer risks than twin pregnancies. They develop into foetuses and are born normally, so a number of identical cloned animals are produced by different mothers.

In pigs, why must a number of cloned embryos be introduced into each mother pig?

Because they naturaly produce a little of piglets, and the body may reject and reabsorb a single foetus.

What does the technology of artificial twining in animals make possible?

It makes it possible to greatly increase the numbers of offspring produced by the animals with the best genetic stock. Some of the embryos may be frozen. This allows the success of a particular animal to be assessed, and if the stick is good, the remaining identical embryos can be implanted and brought to term.

What does artifical twinning clone?

An embryo; however, it is now possible to clone an adult animal.

How is is possible to clone an adult animal?

Through somatic cell nucleat transfer.

How does somatic cell nuclear transfer (SCNT) work?

By taking the nucleus from an adult somatic cell and transferring it into an enucleated egg cell (an oocyte which has had the nucleus removed). A tiny electric shock is used to fuse the egg and nucleus, stimulate the combined cell to divide, and form an embryo that is a clone of the original adult.

What is the first step in SCNT?

The nucleus is removed from the somatic cell of an adult animal.

What happens after the nucleus is removed from the somatic cell of an adult animal?

The nucleus is removed from a mature ovum harvested from a different female animal of the same species (it is enucleated).

What happens after the mature ovum is enucleated?

The nucleus from the adult somatic cell is placed into the enucleated ovum and given a mild electric shock so it fuses and begins to divide. In some cases, the nucleus from the adult cell is not removed; it is simply placed next to the enucleated ovum, and the two cells fuse (electrofusion) and begin to divide under the influence of the electric current.

What happens after the nucleus from the adult somatic cell is placed into the enucleated ovum and given a mild electric shock so it fuses and begins to divide?

The embryo that develops is transferred into the nucleus of a third animal, where is develops to term.

What is the new animal formed from SCNT a clone of?

The animal from which the original somatic cell is derived, although the mitochondrial DNA will come from the egg cell.

What is SCNT also known as?

Reproductive cloning, because live animals are the end result. The cloned embryo can hen be split to priduce several identical clones.

What is an example of the problems with the animals produced by SCNT?

Dolly the sheep had to be put down when she was only six years old because she suffered from arthritis and lung disease, usually seen in much older sheep. However, scientists have improved the technique although premature ageing in clones produced by SCNT persists.

What is SCNT used in?

Pharming - the production of animals that have been genetically engineered to produce therapeutic human proteins in their milk. It can also be used to produce GM animals that grow organs that have the potential to be used in human transplants.

Is animal cloning widespread?

No, although it is increasingly used in agriculture and the world of animal breeding and medicine.

What does artificial twinning enable?

High-yielding farm animals to produce many more offspring than normal reproduction.

What are the arguments for animal cloning?

• Artificial twinning enables the success of a sire (the male animal) at passing on desirable genes to be determined. If the first cloned embryo results in a successful breeding animal, more identical animals can be reared from the remaining frozen clones.

• SCNT enables GM embryos to be replicated and to develop, giving many embryos from one engineering procedure. It is an important process in pharming - the production of therapeutic human proteins in the milk of genetically engineered farm animals, such as sheep and goats.

• SCNT enables scientists to clone specific animals, for example, replacing specific pets or cloning top-class race horses. Pet cats and dogs have been cloned in the US at great expense.

• SCNT has the potential to enable rare, endangered, or even extinct animals to be reproduced. In theory, the nucleus from dried or frozen tissue could be transferred to the egg of a similar living species and used to produce clones of species that have been dead for a long time.

What are the arguments against animal cloning?

• Many cloned animal embryos fail to develop and miscarry or produce malformed offspring.

• Many animals produced by cloning have shortened lifespans, although cloned mice have now been developed which live a normal two years.

• SCNT has been relatively unsuccessful so far in increasing the populations of rare organisms or allowing extinct species to be brought back to life.