22.3 Cloning In Animals

Question 1

Describe natural animal cloning (vertebrates)

Answer 1

Animal clones can be produced naturally as a result of sexual reproduction.
During sexual reproduction, once an egg has been fertilised, it’s possible for it to split into multiple embryos with the same generic information (identical/ monozygotic twins)

Question 2

Describe natural cloning in invertebrates

Answer 2

• e.g. starfish can regenerate entire animals from fragments of their body
• however, scientists are now finding that as a result of high mutation rates the offspring are not true clones

Question 3

Two ways we can produce artificial animal clones

Answer 3

• artificial twinning
• somatic cell nuclear transfer

Question 4

Describe and explain the stages of artificial embryo twinning

Answer 4

After an egg is fertilised, it divides to form a ball of cells. Each of these individual cells are totipotent (has the potential to form an entire new animal).

In artificial twinning the split in the early embryo is produced manually .

1) a cow with desirable traits is treated with hormones so she super-ovulated, releasing more mature ova

2) an egg cell is extracted from a female cow and fertilised in a Petri dish

3) the fertilised egg is left to divide at least once, forming an embryo in vitro (outside a living organism)

4) next, the individual cells from the embryo are separated and each is put into a separate Petri dish. Each cell divides and develops normally, so an embryo forms in each Petri dish.

5) the embryos are then implanted into females cows, which act as surrogate mothers. (Each embryo is implanted into a different mother, single pregnancies carry fewer risks than twin pregnancies)

6) the embryos continue to develop inside the surrogate cows, and eventually the offspring are born. They’re all genetically identical to each other.

Question 5

Describe and explain the steps of somatic cell nuclear transfer (SCNT)

Answer 5

1) a somatic cell (any cell that isn’t a reproductive cell) is taken from sheep A. The nucleus is extracted and kept.

2) an oocyte (immature egg cell) is taken from sheep B. It’s nucleus is removed to form an enucleated oocyte.

3) the nucleus from Sheep A is inserted into the enucleated oocyte — the oocyte from sheep B now contains the genetic information from sheep A.

4) the nucleus and the enucleated oocyte are fused together and stimulated to divide (e.g. by electrofusion where an electrical current is applied), this produces an embryo.

5) then the embryo is implanted into a surrogate mother and eventually a lamb is born that’s a clone of sheep A.

Question 6

Uses of animal cloning?

Answer 6

• research purposes
• cloning can be used in agriculture so farmers can increase the number of animals with desirable characteristics to breed from
• can be used to save endangered animals from extinction by cloning new individuals

Question 7

Arguments for animals cloning

Answer 7

• desirable genetic characteristics are always passed on to clones (e.g. high milk production in cows)
• infertile animals can be reproduced
• animals can be cloned at any time (you wouldn’t have to wait for breeding season)
• increasing the population of endangered species helps to preserve biodiversity
• cloning can help us develop new treatments for disease, which could mean less suffering for some people

Question 8

Arguments against animal cloning:

Answer 8

• very inefficient process
• many cloned animal embryos fail to develop and miscarry or produced malformed offspring
  -no genetic variation n clones populations
• difficult, time consuming and expensive
• some may think its unethical, offspring may have a shortened lifespan