Lecture 7: Cloning Flashcards
What is a clone?
A clone is an individual that is genetically identical to another individual
Mechanisms of cloning:
- Natural
- Embryo splitting
- Reprogramming somatic cells
- Nuclear transfer
Natural cloning =
- Asexual reproduction e.g. Hydra
- & Blastomeres in a 2 cell embryo sometimes separate naturally at an early stage, MONOZYGOTIC twins result
Cloning by ‘reprogramming’ somatic cells
- Sometimes differentiation is reversible.
- A carrot root cell can be tricked into forming a new plant that is a clone of the original.
Cloning by nuclear transfer is controversial because:
- the technique is invasive
- there are technical problems
- it gives rise to an ethical dilemma
Two features allow cloning by nuclear transfer:
- The nucleus of every somatic cell contains a complete copy of the individual’s genome
- A fertilised egg is totipotent
totipotent:
of an immature or stem cell capable of giving rise to any cell type or a complete embryo.
how does cloning by nuclear transfer work:
the DNA from one cell is combined with a fertilised egg that has been enucleated
Frog cloning by nuclear transfer:
- Dissociate & Culture adult epidermis
- Obtain nucleus using pipette
- activate & enucleate egg
- cleavage
- complete tadpole
–>When the nucleus of an epidermal cell from an adult frog is transferred into an enucleated egg, a clone of the adult develops
Who were Mega & Morag:
-the first mammals cloned from CULTURED DIFFERENTIATED cells.
-In 1995, Wilmut and Campbell deprived sheep embryo cells of growth factor, which arrested their development
-The DNA was transferred to cytoplasts (enucleated eggs) and stimulated to develop
The early embryos were placed in the uterus of a surrogate. Two lambs were born
Who was dolly?
-The first mammal cloned from ADULT cells
In 1996, Wilmut and Campbell deprived adult sheep mammary gland cells of growth factor to arrest their development
These cells were fused with enucleated eggs, stimulated and transplanted to a surrogate
One lamb, Dolly was born
Method of cloning Dolly:
-cell was obtained form Dorset sheep
-Egg obtained scottish blackface sheep & Enucleated
-colonised & inserted to another scottish blackface sheep
RESUT = 1 sheep, identical to Dorset = DOLLY
Who was Polly?
- the first transgenic mammal clone
- Wilmut & Campbell’s goal - a flock of transgenic sheep that could produce therapeutically useful proteins
- They genetically modified embryo cells and transferred them to enucleated eggs
-7 lambs were born, 3 of which carried the transgene
Polly’s milk contains Human Factor IX, a blood clotting agent used for treating haemophilia
transgenic:
relating to or denoting an organism that contains genetic material into which DNA from an unrelated organism has been artificially introduced.
potential uses of cloning:
- Developmental research, using clones as controls
- Conservation
- Cloning of elite livestock
- Disease resistant farming
- Assisted reproductive techniques
- Therapeutic cloning (Somatic Cell Nuclear Transfer-SCNT)
Potential uses of cloning along with genetic modification:
- Phamring
- xenotransplantation
pharming
he process of genetically modifying plants and animals so that they produce substances which may be used as pharmaceuticals.
Current uses of cloning:
- Many mammals, including mice, cows, and goats, have now been cloned by nuclear transfer.
- Goats and sheep have been genetically engineered to produce useful proteins in their milk
- ANDi = was born with an extra glowing gene called green fluorescent protein (GFP) which is naturally occurring in jellyfish, was taken from a jellyfish and genetically added to ANDi’s DNA sequence through his chromosomes.
conservation cloning examples:
- Banteng calf
- Mouflon Lamb
- Pyrenean Ibex = Only species to have been brought back from extinction (but only for 7 mins….)
problems with cloning for conservation purposes?
- who decides which species should be cloned?
- doesn’t address problem of lost habitat
Misunderstanding of cloning =
Cloning will not bring back a loved one:
- Clones are only DNA clones (not cytoplasm clones)
- Clones have mutations of their own
- Environment is important
problems of cloning=
- Aging- telomeres shorten, once the telomere is gone the organism dies
- Large foetus syndrome and prolonged gestation
- Low success rate (1/277 transnucleated cells for Dolly)
- Lack of genetic variation may lead to disease vulnerability
- For human cloning, psychological problems
Technology is there, understanding is not…
Stem cells are:
are undifferentiated cells that are capable of extensive proliferation.
stem cells produce:
- more stem cells
- differentiated progeny cells
