Cloning in animals

Natural cloning of animals

• Common in invertebrates but in vertebrates --> form of twinning

Cloning in invertebrates

• Starfish can regenerate entire organisms from fragments of the original
• Flatworms and sponges fragment and form new identical animals as part of their normal reproductive process
• Some female insects can produce offspring without mating (not true clones though, significant differences between mothers and daughters)

Cloning in vertebrates

• Monozygotic twins = identical twins
• The early embryo splits to form two separate embryos
• When they're born they may not look identical though - depends on their position in the uterus and the nutrients they received

Artificial clones in animals

• Relatively easy to produce artificial clones of invertebrates - liquidise a sponge or chop a starfish in half
• Vertebrates are harder, especially mammals

Artificial twinning

• After an egg is fertilised it divides into a ball of cell all of which are totipotent (has the potential to divide into an entire organism)
• Artificial twinning = the early embryo is manually split and two or more foetuses are developed
• Used by the farming community to produce the maximum offspring from a particularly good animal

1. A cow with desirable traits is treated with hormones so she super ovulates
2. The ova may be fertilised naturally or by artificial insemination by a bull with desirable traits
3. The early embryos are gently flushed out of the uterus
4. Or the mature eggs are removed and fertilised in the lab
5. Around day 6 the cells are still totipotent so are split into several new embryos 
6. They are then grown in the lab for a few days then inserted into surrogate mothers
7. They develop and are born naturally by different mothers

• In pigs a number of cloned embryos must be introduced to each mother because they naturally produce a litter
• Some of the embryos may be frozen

Somatic cell nuclear transfer (SCNT)

1. The nucleus is removed from a somatic cell of an adult
2. The nucleus is removed from a mature ovum from a different female animal of the same species (it is enucleated) 
3. The nucleus from the adult somatic cell is placed in the enucleated egg cell and given a small electric shock to make them fuse and begin to divide
4. Sometimes electrofusion is used so the somatic nucleus isn't removed 
5. The embryo that develops is transferred into a third animal where it develops
6. The new animal is a clone of the animal from which the somatic nucleus was taken although the mitochondrial DNA will be from the animal the egg cell was from

• New animals from this process often suffer from illnesses shown in older animals of their species (Dolly had arthritis at 6)
• The technique has been improved since Dolly though
• It is used in pharming --> production of animals that have been genetically engineered to produce therapeutic human proteins in their milk
• Used to produce GM animals that grow human organs for transplants

Arguments for animal cloning

• Artificial twinning allows high-yielding farm animals to produce more offspring 
• Artificial twinning enables the success of a male at passing on desirable genes to be determined 
• SCNT enables GM embryos to be replicated and to develop so you get many from one procedure --> important for pharming
• SCNT enables scientists to clone specific animals
• SCNT has potential to enable rare or endangered animals to be reproduced

Arguments against animal cloning

• SCNT is an inefficient process - takes too many eggs to produce a single clone
• Many cloned offspring fail to develop and miscarry or produce malformed offspring
• Many animals produced from cloning have shortened lifespans
• SCNT is relatively unsuccessful so far in increasing populations of rare organisms or allowing extinct species to be brought back to life