Natural cloning of animals

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

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

The nucleus is removed from a somatic cell of an adult
The nucleus is removed from a mature ovum from a different female animal of the same species (it is enucleated)
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
Sometimes electrofusion is used so the somatic nucleus isn't removed
The embryo that develops is transferred into a third animal where it develops
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

Natural cloning in plants