Development 3: Cloning Flashcards
Define clone
individual that is genetically identical to another individual
What are the 4 mechanisms of cloning?
- Natural
- Embryo splitting
- Reprogramming somatic cells
- Nuclear transfer (SCNT)
Describe the natural mechanism of cloning
Asexual reproduction e.g budding = offspring are clones
Twins: Blastomeres in a 2-cell embryo sometimes separate naturally at an early stage = monozygotic twins
Who pioneered the ‘embryo splitting’ mechanism of cloning?
Spemann (1920s)
Describe the ‘reprogramming somatic cells’ mechanism of cloning
- Sometimes differentiation is reversible
- e.g carrot root can be tricked into forming a new plant = clone of original
Describe ‘nuclear transfer’ mechanism of cloning
- Nucleus of every somatic cell contains a complete copy of the individual’s genome
- A fertilised egg is totipotent
- The DNA from 1 cell is combined with a fertilised egg that has been enucleated
= controversial
Describe Megan & Morag, 1995
→ first mammals cloned from cultured differentiated embryo cells
- 1995, Wilmut & Campbell deprived sheep embryo cells of growth factor = 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 → 2 lambs were born
Who was Dolly?
First mammal cloned fully differentiated adult cells
Describe how Wilmut & Campbell (1996) cloned Dolly
- deprived adult sheep mammary gland cells of growth factor = arrested their development
- These cells were fused with enucleated eggs, stimulated and transplanted to a surrogate
- One lamb, Dolly was born
Who was Polly?
the first transgenic mammal clone
What was Wilmut & Campbell’s goal when cloning Polly (first transgenic mammal clone)?
a flock of transgenic sheep that would produce therapeutically useful proteins in their milk e.g Human Factor IX (blood clotting agent to treat hemophilia)
Describe how Wilmut & Campbell produced Polly (trangenic clone)
- They genetically modified embryo cells and transferred them to enucleated eggs
- 7 lambs born, 3 of these carried the transgene
Give some potential uses of cloning
- Developmental research (clones as controls)
- Conservation of extinct species
- Disease resistant farming
- Theraputic cloning
What are some current uses of cloning
- Medical research
- Conservation
What are the problems of cloning by nuclear transfer? (5)
- Ageing → teleomeres shorten, once its gone an organism dies. Clones have the telomeres of their parents = shorter than normal
- Large fetus syndrome and prolonged gestation
- Low success rate
- Lack of genetic variation = disease vulnerability
- Human cloning = psychological problems
