Cloning In Animals Flashcards
what are some examples of natural cloning in invertebrates?
- starfish can regenerate animals from the original if they are damaged.
- flatworms and sponges fragment and form new identical animals as part of their normal reproductive processes, clones of the original.
- hydra produce small buds on the side of their body which develop into genetically identical clones.
- in some insects, females can produce offspring wihout mating (high mutation rates, not true clone. )
what is the main form of cloning in vertebrates?
the formation of monozygotic twins.
how do monozygotic twins form?
early embryo splits to form two seperte embryos.
why might monozygotic twins look different when born?
differences in their position and nutrition in the uterus.
can female amphibians and reptiles produce offspring when no male is available?
Yes but the offspring are often male rather than female so they are not clones of their mother, yet all their genetic information arises from her.
why is it easier to produce artificial clones of some invertebrates?
it is easy to liquidise a sponge or chop up a starfish into fragments.
what are the two methods used in the production of high-quality farm animals?
- Artificial twinning
- somatic cell nuclear transfer.
what are the stages of artificial twinning?
- a cow with desirable traits is treated with hormones so she super-ovulates, releasing more mature ova than usual.
- the ova may be fertilised naturally or by artificial insemination, by a bull with desired traits. early embryos gently flushed out by the uterus.
- alternatively, mature eggs are removed and fertilised by top-quality bull semen in the lab.
- usually 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 a lab for a few days to ensure all is well before it i implanted into a different mother as single pregnancies carry fewer risks than twin pregnancies.
- the embryos develop into foetuses and are born normally, so a number of identical cloned animals are produced by different mothers.
why must a big number of cloned embryos be introduced into each mother pig?
they body may reject and reabsorb a single foeutus.
how does somatic cell nuclear transfer work?
- the nucleus is removed from a somatic cell of an adult mammal.
- the nucleus is removed from a mature ovum harvested from a different female of the same species (it is enucleated.)
- the nucleus from the adult somatic cell is transferred into the enucleated ovum and given a mild electrical shock so it fuses and begins to divide. In some cases, the nucleus from the adult cell is not removed - it can be placed next to the enucleated ovum and the two cells may diffuse (electrofusion) and begin to divide unter the influence of a electrical current.
- the embryo that develops is transferred into the uterus of a third animal, where it develops to term.
- the new animal is a clone of the animal from which the original somatic cell is derived, although the mitochondrial DNA will come from the egg cell.
what is pharming?
the production of animals which have been genetically engineered to produce therapeutic human proteins in their milk.
what are the arguments for artificial twinning?
- artificial twinning enables high-yielding farm animals to produce many more offspring than normal reproduction.
- artifical twinning enables the success of a sire at passing on desirable genes to be determined. if the first cloned embryo resuls in a successful breeding animal, more identical animals can be reared from the remaining frozen clones. the use of meat from animals bored to a cloned parent is now permitted in the US.
what are the arguments for SCNT?
- enables genetically modified embryos to be replicated and to develop, giving many embryos from one engineering procedure. It is an important process in pharming - the production of theraputic human proteins in the milk of genetically engineered farm animals, such as sheep and goats.
- SCNT enables scientists to clone specific animals, replacing specific pets or cloning top-class race horses. pet cats and dogs have been cloned in the US.
- SCNT has the potential to enable rare, endangered, or ven extinct animals to be reproduced. In theory, the nucleus from dried or frozen tissue could be transferred to the egg of a similar living species and used to produce clones of species that have been dead for a long time.
what are the arguments against animal cloning?
- SCNT is a very inefficient process - 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 been developed which live a normal two years.
- SCNT has been relatively unsuccessfu so far in increasing the populations of rare organisms or allowing extinct species to be brought back to life.
how is natual twinning different to artificial cloning?
- natural twinning the early embryo splits. and the two foetuses go on to develop. from the two halves of divided embryo.
- artificial twinning split in early embryo is produced manually.
- the number of identical embryos may be replaced in surrogate mothers to produce a number of high quality animals.
