Development 3: Cloning

Question 1

Define clone

Answer 1

individual that is genetically identical to another individual

Question 2

What are the 4 mechanisms of cloning?

Answer 2

1. Natural
2. Embryo splitting
3. Reprogramming somatic cells
4. Nuclear transfer (SCNT)

Question 3

Describe the natural mechanism of cloning

Answer 3

Asexual reproduction e.g budding = offspring are clones
Twins: Blastomeres in a 2-cell embryo sometimes separate naturally at an early stage = monozygotic twins

Question 4

Who pioneered the ‘embryo splitting’ mechanism of cloning?

Answer 4

Spemann (1920s)

Question 5

Describe the ‘reprogramming somatic cells’ mechanism of cloning

Answer 5

• Sometimes differentiation is reversible
• e.g carrot root can be tricked into forming a new plant = clone of original

Question 6

Describe ‘nuclear transfer’ mechanism of cloning

Answer 6

• 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

Question 7

Describe Megan & Morag, 1995

Answer 7

→ 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

Question 8

Who was Dolly?

Answer 8

First mammal cloned fully differentiated adult cells

Question 9

Describe how Wilmut & Campbell (1996) cloned Dolly

Answer 9

• 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

Question 10

Who was Polly?

Answer 10

the first transgenic mammal clone

Question 11

What was Wilmut & Campbell’s goal when cloning Polly (first transgenic mammal clone)?

Answer 11

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)

Question 12

Describe how Wilmut & Campbell produced Polly (trangenic clone)

Answer 12

• They genetically modified embryo cells and transferred them to enucleated eggs
• 7 lambs born, 3 of these carried the transgene

Question 13

Give some potential uses of cloning

Answer 13

• Developmental research (clones as controls)
• Conservation of extinct species
• Disease resistant farming
• Theraputic cloning

Question 14

What are some current uses of cloning

Answer 14

• Medical research
• Conservation

Question 15

What are the problems of cloning by nuclear transfer? (5)

Answer 15

• 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

Question 16

What are the 2 types of stem cell used in cloning

Answer 16

• Adult
• Embryonic

Question 17

What signal causes stem cells to differentiate?

Answer 17

cytoplasmic

Question 18

Which neurological condition can be treated using stem cells?

Answer 18

Parkinson’s Disease