4. Answer the questions:

1. How was Dolly grown?

2. What did the ABS Global announce?

3. How soon did the general public respond to the news?

4. What did the teenager tell the "Parade" journalist?

5. What does the teenager's reaction show?

6. How are public attitudes about human cloning formed?

7. Why are the prospects for cloning largely positive?

8. What problems would also apply to cloned animals?

9. How long ago did the research on cloning begin?

10) What is one of the main puzzles in developmental biology?

Systems of breeding

1. Read and translate the texts: Cross-breeding.

Cross-breeding is the system of mating animals of different breeds. To be successful it must be planned and the parents must be carefully chosen. When there is no planning or control, the results are usually unsuccessful. Good cross-breeding can give very good results and is used widely in the breeding of nearly every class of stock.

There are two main reasons for cross-breeding. The first is to combine the desirable characteristics of two or more breeds and the second is to get some degree of heterosis or hybrid vigour.

No breed is perfect in every way. Some are well-known for one character, some for another. If good characters of one breed can be combined with the good characters of another breed, it may be possible to produce an animal which is better suited than its parents to a particular market or particular condi­tions.

The offspring from cross-breeding are usually referred to as half-breeds or crosses.

The sheep industry in Great Britain is one of the best examples of planned and efficient cross-breeding. The moun­tain breeds such as Scotch Blackface, Swalesdale, Cheviot and Welsh Mountain are very hardy and very good mothers but they are rather small, not very prolific and their lambs are not suitable for the fat lamb production. Therefore they are crossed with a long-wool ram such as the Border Leicester, Hexham Leicester, Wensleyday or Teeswater that are noted for size and prolificacy.

Cross-breeding can produce new breeds. This type of breed­ing is usually carried out by research stations. It takes many years to produce a new breed. Recent examples are the Colbred breed of sheep. The devel­opment of this breed has taken ten years.

Breeds are also interchanged between countries. The Lin­coln Long-wool was imported from Britain to Australia and crossed with the Merino breed. This combination has resulted in a new breed, the Corriedale which is better suited to Austra­lian conditions and wool production.

Heterosis is the second important reason for cross-breed­ing. The term is used to explain the fact that hybrids or cross­breeds are usually better or more vigorous than their parents.

For example, a recent analysis of 34,000 recorded litters off pigs showed that mating pure-bred sows to a boar of a different breed resulted in 2 per cent more pigs at birth, 5 per cent more pigs at weaning, 10 per cent greater litter weight at weaning compared with pure-bred sows mated to boars of the same breed. Cross-bred sows gave even better results. In other words, there were more pigs born, more of them survived and they grew and thrived better than the pure-breeds. The characters of prolificacy, hardiness and early growth rate are the nods characters included in the term "hybrid vigour".

Mating of Animals of the Same Breed.

There are many breeds in all classes of stock, some being more popular than others. The more popular breeds usually possess one or more valuable characteristics in some high degree. Developing that character within the breed will greatly improve it.

There are two main possibilities to improve the stock by mating them to animals of the same breed. They are using animals that are known to be related or animals that are eith­er not related or very distantly related.