22.3 Cloning in Animals Flashcards
What is natural cloning in animals common in?
Invertebrates
What type of natural cloning occurs in vertebrae’s?
Twinning
What are invertebrates?
Animals which have no spine
How does natural cloning occur in invertebrates?
-Regenerate entire animals from tiny fragments of the original if they are damaged
eg. starfish, flat worms, sponges
-Some produce small ‘buds’ on the side of their body which develop into genetically identical clones
eg. hydra
-Some female insects can produce offspring without mating, however difference can sometimes be found, suggesting high mutation rates, offspring are not true clones
What is the term for identical twins?
Monozygotic twins
How does natural cloning occur in vertebrates?
-Monozygotic twins, early embryo splits to form two separate embryos
-Some female amphibians and reptiles produce offspring without mating when no male is available, offspring often males not females, so not genetically identical clones but all their genetic material arises from her
Why can some monozygotic twins be genetically identical but look different?
Differences in their positions and nutrition in the uterus
What are the two ways of artificially cloning animals?
Artificial twinning
Somatic cell nuclear transfer
What is an ova?
an egg
What is an oocyte?
An immature egg that is not ready to be released from the uterus
What is an enucleated egg cell?
An oocyte with the nucleus removed
What is a somatic cell?
Any cell in the body that isn’t a reproductive cell
Definition of totipotent
A stem cell which can differentiate into any type of cell and form a whole organism
What are the stages of artificial twinning?
- Animal with desirable traits are treated with hormones so they super-ovulate, releasing more mature ova than normal
- The ova may be fertilised naturally or by artificial insemination, by a male with desirable traits
- OR, mature eggs are removed and fertilised by semen in the lab
- Before or around day 6, when cells are totipotent, the cells of the early embryo are split to produce several small embryos
- Each split embryo is grown in a lab for a few days, before being implanted into surrogate mother, each is implanted into a different mother, as single pregnancies carry fewer risks than twins
- Embryos develop in foetuses and are born naturally
In artificial twinning why is each embryo planted into a different surrogate mother?
Single pregnancies carry fewer risks than twins etc.
What are the stages of somatic nuclear transfer?
- A somatic cell is removed from an animal and nucleus is remved
- An oocyte is taken from a different female animal, and its nucleus is removed to create an enucleated egg cell
- Nucleus from adult somatic cell is placed fused with the enucleated egg cell
- A mild electric shock is given so it fuses and begins to divide
- The embryo that develops is implanted into the uterus of surrogate mothers where it develops to term
- The new animal is a clone of the animal from which the original somatic cell is derived, although mitochondrial DNA will come from the egg cell
Why may a clone produced from somatic cell nuclear transferred not be considered an exact cell?
It will contain mitochondrial DNA from the egg cell
What are the uses of animal cloning?
-Research purposes (eg. to test new drugs), because they are genetically identical, the variables that come from genetic differences are removed
-Save endangered animals from extinction
-For agriculture, to increase the number of animals with desirable characteristics to breed from
-Animals that have been GM to produce more useful substances that they don’t normally produces, can be cloned to produce lots of animas which make these substances
-Cloning embryonic stem cells, which have the potential to become any type of cell, to replace damaged tissue in a range of of diseases (eg. spinal cord injury, parkinson’s), if replacement tissue is made by cloned embryonic stem cells, they are genetically identical to patients own cells, wont be rejected
What are the arguments for animal cloning?
-Desirable genetic characteristics are always passed on
-Infertile animals can be reproduced
-Increasing the population of endangered species helps to preserve biodiversity
-Can be cloned at ant time, don’t have to wait till breeding season
-Helps to develop new treatments for disease, less suffering for some people
-High yielding of farm animals, produce more offspring than sexual reproduction
Arguments against animal cloning?
-Can take may eggs to produce a single cloned offspring
-Many have shorter lifespan than natural offspring = some think this is unethical
-Many embryos fail to develop, miscarry and produce malformed offspring
-No genetic variety, all susceptible to the same disease, single disease could wipe them all out
-Using cloned human embryos as a source of stem cells is controversial, emory’s are usually destroyed after the embryonic stem cell has been harvested, some people believe this is destroying a humans life
-Difficult, time consuming and expensive
How has somatic cell nuclear transfer used?
-Pharming, the production of animals which have bee genetically engineered to produce therapeutic human proteins in their milk
-Produce GM animals, which can grow organs that have the potential to be used in human transplants
How does artificial twinning occur differently in pigs?
A number of cloned embryo’s must be introduced into each surrogate as they naturally produce a litter of piglets, if only one foetus is planted, body may reject and reabsorb it
What does artificial twinning make possible?
Allows for an increased number of offspring with the best genetic stock. Some of the embryos may be frozen, allows for the success to be assessed and if stock is good remaining embryos can be implanted
