animal cloning

Question 1

what are the forms of animal cloning

Answer 1

• natural
• artificial

Question 2

what types of animals is natural animal cloning common in

Answer 2

• common in invertebrate animals
• less common in vertebrates but still occur in the form of twinning

Question 3

natural cloning in invertebrates

Answer 3

• can take several forms
• e.g. starfish can regenerate from fragments
• e.g. flatworms and sponges fragment and form new identical animals as part of normal reproductive process
• e.g. hydra produce small buds on the side of their body which develop into genetically identical clones
• scientists are increasingly finding differences between mother and daughters, but suggesting that as a result of high mutation rates the offspring are not true clones

Question 4

natural cloning in vertebrates

Answer 4

• main form is MZ twins
• early embryo splits to form 2 separate embryos
• frequency at which identical twins occur varies between species e.g. domestic cattle rarely if ever produce identical twins naturally while incidence in natural human pregnancies is around 3/1000
• when MZ twins are born they may look different due to their position and nutrition in the uterus
• some female amphibians/reptiles produce offspring when no male is available
• offspring are often male rather than female so not clones of their mother yet all genetic material arises from her

Question 5

artificial clones in invertebrate animals

Answer 5

• relatively easy
• e.g. liquidise sponge or chop up starfish and new animals will generate from most of the fragments

Question 6

2 methods for artificial cloning of vertebrate animals

Answer 6

• artificial twinning
• somatic cell nuclear transfer

Question 7

what is artificial cloning of vertebrates used for

Answer 7

• production of high-quality farm animals
• development of genetically engineered animals for pharming

Question 8

what happens when an egg is fertilised

Answer 8

• divides to form ball of cells
• each of these individual cells is totipotent (has the potential to form an entire new animal)
• as the cells continue to divide, embryo becomes a hollow ball of cells
• soon after this the embryo can no longer divide successfully

Question 9

what happens in natural twinning

Answer 9

• early embryo splits and 2 foetuses go on to develop from the 2 halves of the divided embryo

Question 10

summary of what happens in artificial twinning

Answer 10

• early embryo split is produced manually
• early embryo can be split into more than 2 pieces and results in number of identical offspring

Question 11

what is artificial twinning used in

Answer 11

• used by the farming community to produce the maximum offspring from particularly good dairy or beef cattle or sheep
• like embryo transfer which preceded it
• makes it possible to increase numbers of offspring produced by animals with the best genetic stock and some of the embryos may be frozen to allow success of a particular animal to be assessed and if the stock is good, remaining identical embryos can be planted and brought to term

Question 12

process of artificial twinning

Answer 12

• cow with desirable traits is treated with hormones so she super-ovulates, releasing more mature ova than normal
• ova 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 the mature eggs are removed and fertilised by top-quality bull semen in the lab
• 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 on to form a healthy full-term calf
• 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 different mother as single pregnancies carry fewer risks than twin pregnancies
• embryos develop into foetuses and are born normally, so a number of identical cloned animals are produced by different mothers

Question 13

how does artificial twinning happen in pigs

Answer 13

• a number of cloned embryos must be introduced into each mother pig
• because they naturally produce a litter of piglets, and the body may reject and reabsorb a single foetus

Question 14

how to clone an adult animal instead of an embryo

Answer 14

somatic cell nuclear transfer

Question 15

oocyte

Answer 15

enucleated egg cell

Question 16

Dolly the sheep

Answer 16

• first adult mammal to be cloned using somatic cell nuclear transfer

Question 17

process of somatic cell nuclear transfer

Answer 17

• nucleus is removed from somatic cell of adult animal
• nucleus is removed from mature ovum harvested from a different female animal of the same species (it is enucleated)
• 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, nucleus from adult cell isnt removed and its simply placed next to the enucleated ovum and the 2 cells fuse (electrofusion) and begins to divide under the influence of the electric current
• embryo that develops is transferred to the uterus of a third animal, where it develops to term
• new animal is clone of the animal from which the original somatic cell is derived, although the mitochondrial DNA will come from the egg cell

Question 18

what is somatic cell nuclear transfer also known as

Answer 18

reproductive cloning because animals are the end result

Question 19

how many clones are produced by somatic cell nuclear transfer

Answer 19

the cloned embryo can be split to produce several identical clones

Question 20

issues with animals produced by SCNT

Answer 20

• Dolly had to be put down at 6yo as she had arthritis and lung disease (usually seen in much older sheep)

Question 21

what is SCNT used in

Answer 21

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

Question 22

pros of animal cloning

Answer 22

• artificial twinning enables high-yielding farm animals to produce many more offspring
• artificial twinning enables success of sire (male animal) passing on desirable genes to be determined. if 1st cloned embryo results in a successful breeding animal, more identical animals can be reared from the remaining frozen clones. and use of meat from animals born to a cloned parent is now permitted in the US
• SCNT enables GM embryos to be replicated and develop, giving many embryos from one engineering procedure. its important in pharming to produce therapeutic human proteins in the milk of GM farm animals
• SCNT enables cloning of specific animals e.g. replacing specific pets or cloning top-class race horses
• SCNT has potential to enable rare, endangered, extinct animals to be reproduced as in theory, nucleus from dried/frozen tissue could be transferred to the egg of similar living species and used to produce clones of species that have been dead for a long time

Question 23

cons of animal cloning

Answer 23

• SCNT is inefficient as in most animals it takes many eggs to produce a single cloned offspring
• 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 to live a normal 2 years
• SCNT has been relatively unsuccessful so far in increasing the populations of rare organisms/ bringing extinct animals back to life